Justin Bieber had fans baffled after he challenged Hollywood actor Tom Cruise to a fight on Sunday.

"I wanna challenge Tom Cruise to fight in the octagon. Tom if you dont take this fight your scared and you will never live it down. Who is willing to put on the fight? @danawhite ?" he wrote.

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After the bizarre tweet went viral, MMA fighter Conor McGregor announced that his company would host the fight. 

"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!" McGregor tweeted.

And Twitter lost it! Both Tom Cruise and Justin Bieber have been trending online all Monday morning. The reasons for Bieber challenge is unknown - but fans have already made up their minds as to who would win a fight between the A-Listers.