Julian Castro – one of the final holdouts from the once-vast field of Democratic presidential candidates who had yet to endorse Joe Biden’s presidential campaign – on Tuesday formally backed the former vice president’s White House bid.

Castro, a former San Antonio, Texas mayor who later served as Housing and Urban Development secretary in then-President Barack Obama’s Cabinet, tweeted that “Joe Biden recognizes the urgent need for real reform to address our broken policing system. I’m proud to support him, and I look forward to seeing these reforms become law, so that what happened to George Floyd never happens again.”

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Castro’s endorsement came a couple of hours after Biden – in a major speech amid nationwide protests and riots sparked by Floyd's death in Minneapolis police custody – vowed to reverse the nation’s “systemic racism with long-overdue concrete changes.”

Biden, responding to Castro’s endorsement, tweeted “Julián — I made a promise to George's family that he wouldn't just become another hashtag. We're going to tackle this head on — and we're going to need your help to do it. Grateful for your support.”

While Castro has repeatedly said since ending his own White House bid at the beginning of the year that “I am going to do whatever I can” to defeat President Trump in November, he had not officially backed Biden. Castro's political team told Fox News last Thursday that talks were underway with Biden's campaign toward a formal endorsement of the former vice president.

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With Castro’s endorsement, best-selling spiritual author Marianne Williamson is the only former White House hopeful in the party who’s refrained from endorsing the presumptive Democratic presidential nominee.

Castro and the former vice president – who worked together in the Obama administration – clashed last summer and fall during a couple of Democratic presidential primary debates. Castro was widely panned following the September debate after he apparently questioned the then-76-year-old Biden’s mental acuity.