Michael Bloomberg will address the Democratic National Convention on Wednesday, at which point he is expected to endorse Hillary Clinton for president.

The choice is surprising in some ways. Bloomberg is currently registered as an independent. He was elected mayor of New York City in 2001 as a Republican, but prior to that he had been a registered Democrat. Though his personal political views don’t necessarily align with today’s Democratic party, as the New York Times notes, he has been quite outspoken against Republican nominee Donald Trump throughout this election cycle.

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Bloomberg considered running for president as a third-party candidate earlier this year, but ultimately decided against it. He explained that the process was built to support two parties, and that a third party candidate simply could not win. His speech at the convention is expected to position her as the best choice for moderate voters.

Though he hadn’t endorsed Clinton at the time, he suggested that he didn’t want to unintentionally steal votes away from her, providing Trump with a smoother path towards the White House. “As the race stands now, with Republicans in charge of both Houses, there is a good chance that my candidacy could lead to the election of Donald Trump,” he explained in a Bloomberg View post. “That is not a risk I can take in good conscience.”

Bloomberg specifically spoke out against Trump’s proposal to ban Muslims from entering the country, his promise to deport millions of Mexicans, his refusal to denounce the support of known white supremacists, and his threat to start trade wars with China and Japan. “I love our country too much to play a role in electing a candidate who would weaken our unity and darken our future,” Bloomberg wrote.

Bloomberg has said that the only candidates qualified for the role of president were Jeb Bush, John Kasich, and Hillary Clinton. Clinton is the last one standing of that group, so perhaps the choice to endorse her isn’t all that surprising after all. Considering Trump has convinced voters that he’s qualified for the position based on his experience as a businessman, an endorsement from Bloomberg, a successful billionaire businessman, could help Clinton win over some voters, especially swing voters and moderate Republicans wary of a Trump presidency.

“As the nation’s leading independent and a pragmatic business leader, Mike has supported candidates from both sides of the aisle,” Howard Wolfson, senior advisor to Michael Bloomberg, told Fortune. “This week in Philadelphia he will make a strong case that the clear choice in this election is Hillary Clinton.”