WASHINGTON — At the time, it seemed mildly noteworthy, but not particularly unusual: then-Vice President Joe Biden, traveling to China on an official visit, had brought his son Hunter Biden along.

And when the two appeared in public together in Beijing during the 2013 trip, there were all the typical trappings of a mini-family vacation tacked on to a business trip.

With granddaughter Finnegan in tow, the Biden men sipped tea in a Confucian-style teahouse, leafed through books at local shops and treated themselves to mid-afternoon ice cream.

But almost six years later, Biden’s trip to Beijing is coming under new scrutiny amid revelations about President Donald Trump’s efforts to dig up information to corroborate his unproven corruption allegations regarding Biden and his son’s work in Ukraine.

In 2013, I was one of four reporters who traveled aboard Air Force Two with Biden and his son to China, a visit that was sandwiched between stops in Japan and South Korea. When we got on the plane on a bright Sunday afternoon at Joint Base Andrews, the Bidens were already on board, having just flown in from a family Thanksgiving gathering in Nantucket. Biden often took family members and especially his grandchildren on his foreign trips, so their presence didn’t raise eyebrows.

What wasn't known then was that as he accompanied his father to China, Hunter Biden was forming a Chinese private equity fund that associates said at the time was planning to raise big money, including from China. Hunter Biden has acknowledged meeting with Jonathan Li, a Chinese banker and his partner in the fund during the trip, although his spokesman says it was a social visit.

The Chinese business license that brought the new fund into existence was issued by Shanghai authorities 10 days after the trip, with Hunter Biden a member of the board.

Seeking to expand his corruption accusations beyond Ukraine, Trump has accused Hunter Biden of using his trip on Air Force Two to procure $1.5 billion from China for his fund, calling it “a horrible thing.”

Despite Trump's accusations, there has been no evidence of corruption on the part of the former vice president or his son.

Hunter Biden’s spokesman, George Mesires, told NBC News that Hunter Biden wasn’t initially an “owner” of the company and has never gotten paid for serving on the board. He said Hunter Biden didn’t acquire an equity interest in the fund until 2017, after his father had left office.

And when he did, he put in only about $420,000 — a 10 percent interest. That puts the total capitalization of the fund at the time at about $4.2 million — a far cry from the $1.5 billion that Trump has alleged.

"The Washington Post Fact Checker has dismantled this conspiracy theory,” said Andrew Bates, spokesman for Joe Biden's presidential campaign. “Donald Trump's degradation of his office is unacceptable.” The Post's fact-check traced the origins of the $1.5 billion figure to a 2018 book published by conservative author Peter Schweizer.

Still, Hunter Biden's participation in the trip has raised additional questions about why the elder Biden, while in office, did not do more to ensure his son’s overseas business interests did not intersect with his work as vice president, or at least avoid the perception of potential conflicts of interest.

“I have never spoken to my son about his overseas business dealings,” Biden said last month.

Throughout the weeklong trip, Hunter Biden seemed to duck in and out, sometimes joining his father at events and red-carpet arrival ceremonies, and at other times following his own itinerary, presumably with his daughter Finnegan. As is customary, the White House did not provide details about what the vice president’s relatives were doing when they were not part of his public events.

Hunter Biden was with his father when Air Force Two touched down in Beijing, sporting a black pea coat as he walked down the stairs behind his daughter and the vice president, who wore his signature aviator sunglasses. A Chinese military honor guard was waiting at the bottom of the staircase, along with top U.S and Chinese diplomats.

Vice President Joe Biden speaks with Chinese Vice Premier Li Yuanchao before a lunch in Beijing on Dec. 5, 2013. Andy Wong / Reuters file

For the vice president, there was plenty of serious business to attend to in China. The Obama administration was struggling to prove that it was following through on its Asia “rebalance,” a strategy U.S. officials would only privately acknowledge was intended to counter China’s influence. A crisis in the region over a controversial Chinese air defense zone had thrust Biden into the role of trying to persuade Beijing to back down.

In fact, the biggest tension point between the vice president’s office and journalists accompanying Biden on the trip was over the media’s coverage of his five and a half hours of talks with Chinese President Xi Jinping. Reporters had described Biden as “somber” or “subdued” during a photo-op, suggesting the meeting may not have gone well.

“Candor generates trust,” Biden told Xi during the photo-op. “Trust is the basis on which real change — constructive change — is made.”

It was about midnight by the time Biden’s marathon meetings with Xi wrapped up, and Hunter Biden wasn’t present for the meeting. But by the next afternoon, he and his daughter had linked back up with the vice president, joining him for some family time in Beijing’s Dongcheng District, a bustling shopping district not far from Tiananmen Square.

Trailed by a throng of photographers and curious locals, the Bidens spent roughly an hour perusing gift shops, buying Magnum ice cream bars from a street vendor and discussed holiday presents for relatives loudly enough that the journalists with them could hear. Hunter Biden, in an apple-red sweater and white collared shirt, also joined his daughter and father for an elaborate traditional tea ceremony involving “white tea” leaves dried in sunlight and “blue tea” leaves dried in moonlight.

Several former White House officials who traveled with Biden on the trip told NBC News that they didn’t know at the time that Hunter Biden had any business interests in China and were unaware of his private schedule while in Beijing.

They said there were no indications the younger Biden had connected his work to his father’s government position. “It just wasn’t something that was on any of our radar screens,” said Jake Sullivan, who was Biden’s national security adviser at the time. “Hunter’s presence didn’t really factor into anything the vice president and the team were thinking about from a policy or diplomacy perspective.”

What else Hunter Biden may have done during the two-day stop in China is unclear. There are no indications he met with Chinese government officials. Mesires, the spokesman, said that he did not conduct any business during the trip — including when he met with Li, the Chinese banker and his nascent business partner.

“How do I go to Beijing, halfway around the world, and not see them for a cup of coffee?” the younger Biden told The New Yorker earlier this year.

Mesires said the fund been in the works for months before the China trip. He said Hunter Biden didn’t take an active role in decisions about establishing the company, whose initial formation documents were filed in November 2013 — the month before the China trip.

In August, Senate Finance Committee Chairman Chuck Grassley, R-Iowa, raised concerns about Hunter Biden’s meeting with Li in a letter to Treasury Secretary Steven Mnuchin that warned of Hunter Biden’s “history of investing in and collaborating with Chinese companies.” Grassley’s letter also cited media reports saying Hunter Biden had arranged for Li, his business partner, to shake hands with the vice president while in Beijing.

Also involved in the fund is Devon Archer, a past adviser to former Secretary of State John Kerry, who also partnered with Hunter Biden on his work in Ukraine and a U.S. investment firm.

The renewed interest in the China trip comes as Trump faces an impeachment inquiry from the House after a whistleblower in the intelligence community brought attention to a July 25 call between Trump and Ukrainian President Volodymyr Zelenskiy. Trump, in the call, pressed the Ukrainian leader to investigate Biden and his son as a “favor” and seemed to link it to the sale of Javelin missiles by the U.S. to the Ukrainians.

Democrats say that constituted an abuse of Trump’s presidential powers for political purposes given Biden’s position as a top contender for the Democratic presidential nomination.

And Trump, too, has come under scrutiny for potential conflicts between his presidential duties and his family’s overseas business interests — including in China. Authorities in China have granted dozens of trademarks since Trump took office to the brand of his daughter and senior White House adviser Ivanka Trump, even as the president is engaged in high-stakes trade talks with Beijing.