Elon Musk will interview former President Donald Trump on Monday evening on social media platform X, the latest collaboration between two men whose unlikely alliance could be a significant factor shaping the final weeks of the presidential race.

“This is unscripted with no limits on subject matter, so should be highly entertaining!” Musk, the billionaire CEO of both Tesla and SpaceX, wrote in a Sunday post on X. The event is scheduled for 8 p.m. ET and will be streamed on X, which Musk owns.

Hours ahead of the interview, Trump posted a campaign ad on his personal X account. It marked the first time since August 2023 that Trump has posted anything on X.

The former president typically restricts his social media activity to Truth Social, the conservative-friendly platform owned by his eponymous media venture, Trump Media & Technology Group.

Trump helped to create Truth Social and later made it his primary platform, after he was suspended from then-Twitter and Facebook following the Jan. 6 Capitol insurrection.

As part of his contract with the new company, Trump agreed to stop posting content on Twitter, now X, that he had not already posted on Truth Social. But the agreement has a loophole: Trump is always allowed to use his personal X and Facebook accounts for any posts that are political in nature or campaign-related, according to a company financial filing.  

Trump’s return to X on Monday revived the prospect that he might start posting more regularly to the platform that was so instrumental to his political rise — now that it is owned by a friendly Musk.

Shares of Trump Media were down 5% at Monday’s market close ahead of the conversation with Musk.

Musk posted on X that he planned to perform “some system scaling tests” to gauge the X platform’s streaming capabilities ahead of the event with Trump.

The tests are intended to prevent a repeat of the disastrous May 2023 live launch of Florida Gov. Ron DeSantis‘ presidential campaign, which was held on the social media platform. The webcast glitches derailed the highly anticipated event.

Earlier this year, Musk created the America PAC, a pro-Trump political action committee that Musk reportedly had planned to bankroll with as much as $45 million a month. Musk later denied that he ever intended to give that much.

The PAC set out to mobilize 800,000 voters for Trump in critical swing states. But after a rocky start and high turnover, CNBC reported that the PAC is facing questions from state election officials about how it collects and uses voters’ personal information.

While the fate of the PAC is unclear, the conversation Monday night could provide a welcome boost for Trump at a crucial moment for the Republican presidential nominee.

Just three weeks after Vice President Kamala Harris‘ surprise entry into the race, the Democrat has erased Trump’s polling lead and shifted the momentum of a contest that had looked, at one point, like it was Trump’s to lose.

A buzzy, newsmaking event with Musk could help to reinvigorate Trump’s base voters.

As recently as 2022, Musk and Trump were public enemies, trading insults on social media and at political rallies.

“I don’t hate the man, but it’s time for Trump to hang up his hat & sail into the sunset,” Musk wrote on social media in July 2022.

The next day, Trump clapped back at Musk on Truth Social:

“When Elon Musk came to the White House … I could have said, ‘drop to your knees and beg,’ and he would have done it …” Trump wrote.

Two years on, the two appear to have buried the hatchet.

Musk endorsed Trump in July, within hours of an assassination attempt at a Pennsylvania rally that left the former president with a minor bullet wound on his ear and killed an audience member.

In turn, Trump appears to have changed his tune on Musk. He has even softened his critiques of electric vehicles.

“I love Elon. He’s great,” Trump said at the Bitcoin Conference in Nashville last month. “He endorsed me, and great endorsement and everything else. But not everybody has to have an electric car.”

This is a developing story. Check back for updates.