John Podesta’s biggest regret on leaving the White House is not proving Fox Mulder right.

“My biggest failure of 2014: Once again not securing the #disclosure of the UFO files,” he tweeted on Friday, his final day as counselor to President Obama.

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He added the hashtag “#thetruthisoutthere,” in a reference to the long-running television show “The X-Files.”

Podesta is leaving the White House on Friday after one year helping to oversee climate change and energy policy, among other issues, and is seen as a likely choice to lead Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE’s expected presidential campaign. He formerly worked as chief of staff to President Bill Clinton William (Bill) Jefferson ClintonBarr says Ginsburg 'leaves a towering legacy' Trump reacts to Ginsburg's death: 'An amazing woman who led an amazing life' Jimmy Carter remembers Ruth Bader Ginsburg as 'a beacon of justice' MORE before starting the liberal Center for American Progress think tank.

The humorous tweet about his time in office came in a list of his top 10 moments over the last year, including the landmark joint agreement between U.S. and China to reduce carbon emissions and an effort to protect people’s privacy amid the rise of “big data” in the digital age.

“It's been a tremendous privilege to serve a great President and the country for this last year,” he tweeted.

Podesta is being replaced by Brian Deese, the deputy director of the White House budget office.