Metro Manila (CNN Philippines, May 11) — Maria Lourdes Sereno has become the first Chief Justice to be ousted by the Supreme Court.

In a landmark ruling Friday, eight justices voted to grant Solicitor General Jose Calida's petition to unseat Sereno. These were Teresita de Castro, Diosdado Peralta, Lucas Bersamin, Francis Jardeleza, Samuel Martires, Noel Tijam, Andres Reyes, and Alexander Gesmundo.

The six against it were Senior Associate Justice Antonio Carpio, Associate Justices Presbitero Velasco, Mariano Del Castillo, Estela Perlas-Bernabe, Marvic Leonen, and Alfredo Benjamin Caguioa.

The decision was announced by Supreme Court Spokesperson Theodore Te after an en banc session that Sereno attended.

Sereno is "found disqualified from and is hereby adjudged guilty of unlawfully holding and exercising the office of the Chief Justice," according to the decision signed by Tijam and read by Te in a media briefing.

The Supreme Court said its ruling is "immediately executory," although Sereno has 15 days to appeal the decision.

"The position of the Chief Justice is declared vacant and the Judicial and Bar Council is directed to commence the application and nomination process," it added.

President Rodrigo Duterte, who had declared himself an enemy of Sereno and called for her ouster, will appoint the next chief justice.

Calida, the government's top lawyer, in March slapped Sereno with a quo warranto petition, a legal proceeding where an individual's right to hold office is challenged. It sparked a debate on whether Sereno as an impeachable official could be removed from office without a Senate trial.

READ: Sereno ouster shows SC bowing to 'aggressive' SolGen – Justice Leonen

The high court, voting 9-5 on Friday said quo warranto was the proper remedy to unseat Sereno. Velasco, de Castro, Peralta, Bersamin, Jardeleza, Martires, Tijam, Reyes, and Gesmundo voted for it.

Nine justices – Carpio, de Castro, Peralta, Bersamin, Jardeleza, Martires, Tijam, Reyes, and Gesmundo – also agreed Sereno violated the Constitution for her failure to file her Statements of Assets, Liabilities, and Net Worth (SALNs) for ten years before she applied for the chief justice post in 2012. This is the main argument raised by Calida in asking for Sereno's ouster.

The Supreme Court gave Sereno 10 days to explain why she should not be sanctioned for her alleged violations.

The ruling comes a month after the high court held oral arguments on the quo warranto petition, where Sereno argued her case and vowed to present her missing SALNs only before the Senate impeachment court.

But her ouster at the Supreme Court preempts what could have been a Senate trial if 1/3 of the members of the members of the House of Representatives voted to impeach her.

READ: Unseating Sereno: A tale of two ousters

Is there hope for Sereno?

Sereno's camp said they are "very likely" to ask for a reconsideration.

"There is hope," Josa Deinla, one of Sereno's spokespersons told CNN Philippines.

Presidential Legal Counsel Sal Panelo agreed Sereno is entitled to file for reconsideration, saying "she still has a chance."

But Integrated Bar of the Philippines President Abdiel Fajardo said motions for reconsideration usually "have very slim chances of success in the Supreme Court.

The Palace said the Supreme Court's decision should be respected.

"The Supreme Court, a co-equal branch of government, is duty-bound to uphold the Constitution. The court ruling is likewise an assertion of the supremacy of the fundamental law of the land," Presidential Spokesperson Harry Roque said in a statement.

Calida praised the magistrates for their decision which he said was the "epitome of (the High Court's) exercise of judicial independence."

"The Supreme Court Decision ousting Maria Lourdes Sereno augurs well for the country as it preserved the stability and integrity of the Judiciary," he said in a statement.

READ: Robredo: Sereno ouster compromised the foundation of the judiciary

Sereno: We actually won

But Sereno, addressing her supporters hours after the unfavorable decision, said she should have won the case if only six associate justices – Peralta, Bersamin, Jardeleza, Tijam, de Castro, and Martires – inhibited from voting. She had asked them to inhibit from the case, but all denied her plea and voted against her.

Sereno insists only the eight other justices' votes should have been counted.

"Kung tutuusin panalo po tayo. Anim po sa natitirang walo ang nagsabing hindi ako dapat alisin. Dalawa lamang po ang bumoto na ako ay dapat alisin," she said.

[Translation: "We actually won. Six of the remaining eight justices said I should stay. Only two voted for my ouster."]

She said she will continue to fight for justice. "Ang araw na ito ay hindi katapusan, kung hindi simula lamang... Ang araw na ito ang araw ng paglaban (This is just the start, not the end. This is day marks the start of the fight.)," she said.

Sereno had gone on an indefinite leave on March 1 at the request of all 13 justices present in a February 27 en banc session. She returned to work on May 9, and was seen working in her office hours before her colleagues decided her fate before noon on Friday.

Sereno ouster vote

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Supreme Court is set to vote on Chief Justice Sereno's ouster today. CNN Philippines gives you updates as they happen.

CNN Philippines' Anjo Alimario contributed to this report.