Hunter Biden, the president-elect's embattled son, announced Wednesday that federal prosecutors in Delaware are investigating his "tax affairs," a development that marks the latest controversy surrounding the Biden family's private business endeavors.
Federal investigators are looking into Hunter's business dealings in China and elsewhere, including scrutinizing whether he may have committed tax crimes stemming from those overseas business dealings.
In a statement released through the Biden-Harris transition team, Hunter Biden, 50, said he and his attorney learned of the investigation on Tuesday, and that he remains "confident that a professional and objective review of these matters will demonstrate that I handled my affairs legally and appropriately, including with the benefit of professional tax advisors."
The probe predates by more than a year the attacks leveled by Trump and his supporters during the campaign, according to a source familiar with the matter.
A separate source with knowledge of the investigation said the tax probe began in 2018, and that the U.S. Attorney's Office in Delaware waited to notify Hunter Biden's legal team due to sensitivities around the 2020 presidential election.
In fact, the investigation was put on pause for several months while the Democratic primaries and then the general election campaigns played out.
A Biden transition spokesperson did not respond to multiple inquiries about why the president-elect's office would issue a statement on behalf of Hunter Biden, who is not expected to join the administration, as opposed to a statement coming from Hunter Biden's private legal counsel. The Trump family has faced scrutiny from ethics watchdogs who accused them of blurring the line between politics and business.
Officials with both the U.S. Attorney's Office in Delaware and the FBI declined to comment when contacted by ABC News. A lawyer for Hunter Biden did not immediately respond to ABC News' request for comment.
A source familiar with Hunter Biden's tax probe said investigators are particularly interested in a 2.8-carat diamond he received from a Chinese business associate in 2017.
According to Hunter Biden, the diamond was offered to him as a gift from Ye Jianming, the former head of CEFC China Energy, as Hunter sought to lock in a donation from Ye to the U.N. World Food Programme.
"I was, like, 'Oh, my God,'" Hunter told the The New Yorker magazine last year, describing the delivery of the diamond to his hotel room in Miami in 2017.
"I knew it wasn't a good idea to take it. I just felt like it was weird," he added, insisting he then gave the diamond to two of his associates.
The diamond reemerged as a point of conflict in his divorce proceedings with ex-wife Kathleen Biden, who claimed it was worth $80,000. Hunter Biden told The New Yorker it was likely closer to $10,000.
Beyond that, Hunter Biden's relationship with Ye Jianming runs far deeper than the bizarre diamond interlude.
The Senate Homeland Security and Government Affairs probe into Hunter Biden's overseas work described Ye as "a Chinese businessman and a frequent figure in Hunter Biden's financial dealings in China." The report also described multiple instances in which multimillion-dollar wire transfers between Ye, his corporate entities, his subsidiaries and Hunter Biden were "identified for potential criminal financial activity," citing confidential documents.
In its report, the committee did not accuse Hunter Biden of any specific illegal activity.
Ye was detained by Chinese authorities in 2018 for "suspected economic crimes," and has not been seen publicly since.
Scrutiny of Hunter Biden's finances and business dealings first emerged shortly after his father announced his bid for the presidency in the spring of 2019.
Candidate Biden denied that, saying that he and his son never discussed his son's business.
In July of 2019, President Trump encouraged Ukrainian President Volodymyr Zelenskiy to investigate the Bidens -- a blending of the president's foreign policy work and his own political goals that prompted the congressional impeachment inquiry. Trump was impeached by a Democrat-controlled House for abuse of power and obstruction of Congress, and was later acquitted by the Republican-controlled Senate on a partisan vote.
While government watchdogs have broadly taken issue with the ethical implications of Hunter Biden's foreign business dealings, Wednesday's development marks the first instance in which the legality of Hunter Biden's finances have been called into question.
The Biden transition team released a statement of support for Hunter Biden on Wednesday, noting that the president-elect remains "deeply proud of his son, who has fought through difficult challenges, including the vicious personal attacks of recent months, only to emerge stronger."