Justin Bieber has challenged Tom Cruise to a UFC fight

Who knows what he's done to get on the wrong side of Justin Bieber, but the pint-sized pop star has offered Tom Cruise outside.

In a tweet appealing for a promoter to lay on the scrap, Bieber took to Twitter to challenge Cruise to a televised duel of pugilism, for reasons known only to himself.

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“I wanna challenge Tom Cruise to fight in the octagon,” the 25-year-old Bieber tweeted at the 56-year-old screen legend.

“Tom if you don’t take this fight you’re scared and will never live it down. Who is willing to put on the fight?”

Bieber also tagged Dana White into the message, the president of the Ultimate Fighting Championship.

As if that wasn't quite strange enough already, UFC champ Conor McGregor then decided to chime in, offering to host.

“If Tom Cruise is man enough to accept this challenge, McGregor Sports and Entertainment will host the bout. Does Cruise have the sprouts to fight, like he does in the movies? Stay tuned to find out!” he tweeted.

Stranger still, then this happened:

“I challenge Mark Wahlberg on the very same card,” McGregor added.

“Back when Mark Wahlberg was Marky Mark, I’d’ve still slapped the ears off him and took my UFC shares back.”

WHAT IS GOING ON.

Wahlberg does indeed own shares in UFC, along with a host of other celebrities including Ben Affleck, LL Cool J, Tyler Perry, South Park creator Trey Parker, Sylvester Stallone and the Williams sisters.

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Tom Cruise is busy shooting Top Gun 2, so it could be that the Bieber fight could be difficult to schedule for the moment.

But could this be the beginning of a rash of celebrity UFC challenges?