Only a few days after Deontay Wilder’s commanding WBC title defense with a ruthless first-round KO of Bermane Stiverne, Wilder has issued his next challenge. This time, though, it’s to a far more formidable opponent: Anthony Joshua.

In a new Instagram video, Wilder issued a challenge to the undefeated British heavyweight, telling him to “fight or shut up”.

Wilder has won all 39 of his fights with relative ease. But if he gets his wish and his 40th features Joshua, his time in the ring will almost certainly be more difficult than Saturday’s first-round KO of Stiverne. Joshua is the holder of the IBO, WBA, and IBF heavyweight championship belts, and sports a 20-0 record.

If Wilder and Joshua were to finally meet—and it’s looking increasingly likely that they will—it would be an epic battle to become the best heavyweight on the planet. Joshua has already said the fight will be “on his terms,” and that promoter Eddie Hearn would extend an offer to Wilder.

Also of note: When Stiverne first faced Wilder in 2015, Stiverne went the distance, making him the only man who’s ever faced off against Wilder without getting knocked out. This time, though, Stiverne was severely outmatched by the “Alabama Slammer”. (In fairness, Stiverne was asked to fill in last-minute for Wilder’s original opponent, who was removed due to PED violations.)

Check out Wilder’s intimidating threat to Joshua below.