Here we go.

After Elon Musk recently tweeted that he would be “up for a cage fight” with Zuckerberg, the Meta CEO shot back by posting a screenshot of Musk’s tweet with the caption “send me location.”

I’ve confirmed that Zuckerberg’s post on his Instagram account is, in fact, not a joke, which means the ball is now in Musk’s court. “The story speaks for itself,” Meta spokesperson Iska Saric told me.

Musk has responded, with two words: Vegas Octagon.

The backstory here: since I recently reported more details about Meta’s forthcoming Twitter competitor, Musk has been taunting Zuckerberg on Twitter with zingers like “Zuck my 👅.” During an internal all-hands meeting at Meta last week, chief product officer Chris Cox told employees the company thinks creators want a version of Twitter that is “sanely run,” drawing cheers. “I’ve always thought that Twitter should have a billion people using it,” Zuckerberg said during a recent podcast interview with Lex Fridman.

In terms of tech billionaire CEOs literally fighting, Musk versus Zuckerberg would be as good as it gets. Musk, 51, has the upper hand on Zuckerberg in terms of sheer physical size, and he has talked about being in “real hard-core street fights” when he was growing up in South Africa. Meanwhile, Zuckerberg, 39, is an aspirational MMA fighter who is already winning Jiu-Jitsu tournaments. He also claims to have recently completed the grueling “Murph Challenge” workout in just under 40 minutes.

Regardless of who would win, I think we can all agree that a Musk-versus-Zuckerberg match would be one of the most entertaining fights of all time. It needs to happen. Don’t back down now, Musk.

Update June 21st, 10:30PM ET: Added response from Elon Musk.