Bernie Sanders endorsed former foe Joe Biden for president in a livestreamed event Monday — handing a powerful boost to the ex-veep as he battles to unify their divided party.

“We must come together to defeat the most dangerous president in modern history,” Sanders tweeted along with a link to their appearance.

The liberal US senator from Vermont, 78, told Biden, 77, at the start of the online chat, which featured split-screen appearances by the pair, “I am asking all Americans, I’m asking every Democrat, I’m asking every independent, I’m asking a lot of Republicans, to come together in this campaign to support your candidacy, which I endorse.”

Biden — hoping to woo Sanders’ fiercely loyal corps to his side in a bid to beat President Trump in November — assured the senator’s supporters that he would be advising him on key issues including the economy, education and health care.

“Bernie, I’m gonna need you,” Biden acknowledged to Sanders, a former lingering key primary-race holdout. “You’ve been maybe the most powerful voice for every generation of Americans.”

In a clear nod to just how crucial Sanders’ supporters are to his election bid, Biden later insisted to them in a tweet, “To Bernie’s supporters: I see you, I hear you, and I understand the urgency of what it is we have to get done in this country.

“I hope you will join us. You are more than welcome on this campaign. You’re needed.”

Biden said during the duo’s online appearance that the senator would be leading “six policy working groups” to advise him on the economy, education, health care, criminal justice reform, immigration and climate change.

“You and I have been friends. We’ve disagreed, but we’ve been friends,” Biden said. “And I promise I will not let you down.”

Sanders said, “I know you’re the kind of guy who’s gonna be inclusive.”

On their disagreements, Sanders added, “We can argue it out. It’s called democracy.”

Biden asked Sanders what he could do to reach millennials.

Sanders responded by urging Biden to “make public education and colleges free.”

Biden agreed to at least overhaul the college loan system and claimed that his late son Beau “is still paying off his loans.”

The former vice president also suggested creating a “new cabinet office on pandemics” amid the coronavirus crisis.

The pair, who heatedly sparred during primary debates, joked cordially during the online chat.

“I thought we’d play some chess, what do you think?” Sanders asked Biden at one point.

Biden replied, chuckling, “I’d like to play some chess.”

But some Sanders supporters later balked online at now backing Biden.

“Bernie made us believe our power was the collective, us, not the individual me,” tweeted a Bernie bro. “I love Bernard Sanders, a true inspiration whose message and lessons I will carry with me for the rest of my life. But, we, ‘us’ do not support Joe Biden. Because Joe Biden does not support us.”

Another Twitter user was more supportive.