Don't You Worry Child Swedish House Mafia
The music mogul has finally signed up and racked up 175,000 followers in a matter of hours.
After signing up @SimonCowell tweeted:
"It's official, I know it's taken a while. It's really me! We're live in 10 minutes. I'll keep you posted. Lots of love #iamsimon. [sic]"
However, it didn't take the 52-year-old long before got the claws out when tweeting his fellow US X-Factor judges.
"I love being on twitter. Thank you for allowing me to beat the other 3 in the popularity poll. Paula looked like she'd sucked on a lemon! [sic]"
He also went on to claim that the female judges were threatened by one of his acts, 14-year-old Drew Ryniewicz.
"Drew was amazing. The girls @PaulaAbdul and @NicoleScherzy are threatened by her."
Simon also quickly became embroiled in a spat with former America's Got Talent judge Piers Morgan, who's notorious for winding up Twitter 'newbies'.
Morgan tweeted: "At last! Bring. It. On. love #iampiers. Save your breath @SimonCowell - nobody's watching X Factor, my show's about to start #CNN @PiersTonight."
Cowell hit back: "@piersmorgan look up the word deluded in your dictionary."
Piers then said: "Comes before 'demolished' - ironically what I'll do to you on here."
The war of words continues...