Former New York mayor Michael Bloomberg will endorse Hillary Clinton for president at the Democratic National Convention next week.

He will make his speech at the DNC on Wednesday night, Bloomberg spokesperson Marc LaVorgna told the Associated Press on Sunday. He will attempt to make the case for Clinton to moderate voters in the prime-time slot.

The move comes as a surprise to many, as the billionaire media mogul has not been a registered Democrat since 2000. He switched to the Republican party before successfully running for mayor in 2001, and served three terms. He later became an independent and an advocate for gun control.

“As the nation’s leading independent and a pragmatic business leader, Mike has supported candidates from both sides of the aisle,” Bloomberg senior adviser Howard Wolfson told the New York Times, which first reported the news. “This week in Philadelphia he will make a strong case that the clear choice in this election is Hillary Clinton.”

Bloomberg gave up his own shot at a run for the presidency earlier this year. Speculation had swirled that he would campaign for president as a third-party candidate, but he announced in March that he would not run, fearing that it would help Donald Trump, who was then the Republican frontrunner and is now the official candidate, in taking away votes from Clinton.

Bloomberg has been openly critical of Trump through this election cycle. He has especially taken aim at Trump’s controversial rhetoric on immigration.