(CNN) Even French investigators are now convinced: The airplane debris found on Reunion Island in July belongs to vanished Malaysia Airlines Flight 370, a top French prosecutor said Thursday.

Investigators learned Thursday that a series of numbers found inside the plane flaperon matches records held by a Spanish company that manufactured portions of the component, linking the debris to MH370, the office of Paris Prosecutor Francois Molins said.

"Consequently, it is possible today to affirm with certainty that the flaperon discovered at the Reunion Island on July 29, 2015, is that of MH370," the office said.

The announcement slices the last thread of public reservation that Molins' office had about whether the debris was linked to the Boeing 777 that disappeared with 239 people aboard in March 2014.

Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference at a hotel in Sepang on March 8, 2014. "We deeply regret that we have lost all contacts" with the jet, he said.

Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference at a hotel in Sepang on March 8, 2014. "We deeply regret that we have lost all contacts" with the jet, he said.

Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8, 2014.

Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8, 2014.

A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014.

A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014.

Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014.

Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014.

The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014.

The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014.

Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014.

Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014.

A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand.

A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand.

A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014.

A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014.

A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014.

A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014.

Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014.

Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014.

A Vietnamese military official looks out an aircraft window during search operations March 13, 2014.

A Vietnamese military official looks out an aircraft window during search operations March 13, 2014.

Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean.

Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean.

U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014.

U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014.

On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet.

On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet.

A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014.

A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014.

Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight.

Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight.

Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search.

Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search.

A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia.

A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia.

Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived."

Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived."

People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014.

People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014.

A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014.

A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014.

The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions.

The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions.

On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370.

On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370.

A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014.

A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014.

A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014.

A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014.

Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014.

Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014.

A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014.

A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014.

The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014.

The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014.

A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014.

A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014.

Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014.

Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014.

Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public.

Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public.

A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane.

A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane.

Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead.

Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead.

In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was.

In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was.

Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft.

Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft.

On July 29, police carry a piece of debris on Reunion Island, a French territory in the Indian Ocean. A week later, authorities confirmed that the debris was from the missing flight.

Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board.

Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board.

The Malaysian Prime Minister said weeks ago that the debris, found in July on the shores of the French island in the Indian Ocean, clearly was from MH370. French investigators, however, had said that further testing was needed to say that with ironclad confidence. Some passengers' relatives agreed, saying they wanted more proof.

French investigators now believe they have it. France, which already had launched a criminal probe into the disappearance because four French nationals were aboard, sent the debris to a specialized laboratory in Toulouse last month.

Families push for the whole story

Jack Song, brother of passenger Song Chunling, said the piece of debris does not tell then whole story.

"From my opinion, it doesn't matter whether it's from 370 or not," he said. "Because it's just one piece of debris. Not the whole airplane. That doesn't mean anything. Doesn't tell where the plane is or what happened. We need the whole plane, and we need the exact place where the aircraft is."

Molins' office said that experts using an endoscope found three series of numbers inside the flaperon. It appeared, the office said, that the numbers could correspond to a Boeing subcontractor, Airbus Defense and Space in Seville, Spain.

On Thursday, investigators went to Seville and formally linked "one of the three (series of numbers) collected inside the flaperon to the serial number of the Boeing 777 of flight MH370," Molins' office said.

"After a year and a half of ambiguity and disparate theories, I would rather have certainty than doubt," said Sarah Bajc, partner of passenger Philip Wood

" At least now there seems to be evidence that the plane did go in the water. I do wonder why it took so long. I also still wonder where the hull of the plane and the bodies are, and what happened."

K.S. Narendran, whose wife, Chandrika Sharma , was aboard the flight, said the news won't change anything.

"On a daily basis, this news doesn't impact my life. I've had to carry on without a family member and I have gotten used to living without that family member," he said. "Has my life changed between yesterday and today? No. Has my desire to know the truth changed? No, I'd still like to know and I will persist."

The mystery of MH370

In the early hours of March 8, 2014, Malaysia Airlines Flight 370 took off from Kuala Lumpur International Airport in Malaysia en route to Beijing, with 239 passengers and crew on board.

At 1:19 a.m., as the Boeing 777-200ER was flying over the South China Sea, Malaysian air traffic controllers radioed the crew to contact controllers in Ho Chi Minh City for the onward flight through Vietnamese airspace.

The crew's acknowledgment of the request was the last thing ever heard from MH370: "Good night Malaysian three-seven-zero."

Shortly afterward, air traffic controllers in Malaysia lost contact with the plane somewhere over the sea between Malaysia and Vietnam.

The aircraft's transponder, which identifies the plane and relays details like altitude and speed to controllers, stopped transmitting. MH370 seemingly disappeared without a trace.

Malaysian authorities revealed later that military radar had tracked the plane as it turned back to the west and flew across the Malaysian Peninsula, up the Strait of Malacca, before flying out of radar range at 2:14 a.m. and vanishing once again.