Twitter owner Elon Musk and Meta founder Mark Zuckerberg are drawing up plans to tussle each other in a cage fight, after the Tesla CEO threw down the gauntlet on his social media platform.

Musk—who has been known to regret tweets sent after hours—posted late on Wednesday night that he was “up for a cage fight” with Zuckerberg.

A matter of hours later, the Meta founder ominously took to one of his own channels, Instagram, and posted to his story a screenshot of Musk’s tweet captioned “Send Me Location.”

A Meta spokesperson later confirmed to Fortune that Zuckerberg’s response had not been in jest, saying: “The story speaks for itself.”

When alerted to the confirmation Musk similarly doubled down, adding: “If this is for real, I will do it.”

And it appears the richest man on earth has since chosen the place—later tweeting that the Vegas Octagon, a UFC arena, would be the site to host the event. (For the uninitiated, cage fighting is where two fighters in an enclosed space slug it out with a variety of techniques, usually over a three- or five-round bout.)

Although warned by fans that Facebook founder Zuckerberg is training in jujitsu—winning a gold medal in his first tournament earlier this year—Musk seems unperturbed.

He responded to a follower that his signature move is “The Walrus,“ explaining it’s “where I just lie on top of my opponent and do nothing.”

Likewise, Musk seems unbothered by Zuckerberg’s rigorous fitness routine, writing: “I almost never work out, except for picking up my kids and throwing them in the air.”

I have this great move that I call “The Walrus”, where I just lie on top of my opponent & do nothing

— Elon Musk (@elonmusk) June 22, 2023

The Starlink founder’s diet is also not in keeping with that of an athlete, with 51-year-old Musk previously revealing he eats a doughnut every day for breakfast.

Unperturbed, Musk told a user on Twitter the fight would be “hilarious.”

Fans are now flocking to the platform to encourage its chief technology officer, as well as offering training advice and making suggestions about who should referee the match.

This would be hilarious 🤣

— Elon Musk (@elonmusk) June 22, 2023

Calls have been made for high-profile podcaster and former mixed martial arts fighter Joe Rogan—an acquaintance of Musk’s who has interviewed both tech billionaires on The Joe Rogan Experience—to referee the proceedings.

The rise of celebrity fights

The Musk vs. Zuck fight hasn’t sprung out of nowhere—it was prompted by rivalry between the brands owned by the two.

The initial tweet from Musk came in response to an article about the launch of Meta’s Threads—touted as a direct rival to Twitter.

Musk—who purchased Twitter in 2022 and has since seen its value shrink to less than half what he paid—responded: “I’m sure Earth can’t wait to be exclusively under Zuck’s thumb with no other options. At least it will be ‘sane’ [referring to a jibe from Meta product boss Chris Cox]. Was worried there for a moment.”

It’s just the latest example of social media confrontations which may—or may not—result in a physical fight.

Last year YouTuber Jake Paul took on British boxer and social media influencer Tommy Fury in a boxing match in Saudi Arabia, with Paul claiming to have taken home $30 million from the bout despite losing.

The trend in social media bouts has similarly seen clashes between YouTube and TikTok stars—with Austin McBroom taking on Bryce Hall at the Hard Rock Stadium in Miami in 2021.

Other famous faces to have entered the ring include Canadian Prime Minister Justin Trudeau, Kim Kardashian, British actor Idris Elba and Guardians of the Galaxy star Dave Bautista.