The Syco and X Factor boss took time out of his schedule in the USA to watch the ITV1 final and revealed that he backed the public's final vote, which saw the girlband edge out Gary Barlow's act Marcus Collins.
"I was really hoping a group would win this year. [Tulisa] has done a great job. These girls could be stars," he wrote.
Teasing his X Factor USA co-star Paula Abdul, who had the Groups category on the Fox series, he added: "Congratulations to Little Mix. And Paula as you can see, groups can win this show!"
Yesterday, Cowell complimented judge Tulisa Contostavlos and Little Mix for their Alicia Keys mash-up duet performance, commenting: "I think a group may win [The X Factor] for the first time ever... and I think Tulisa should be a permanent fifth member [of Little Mix]!"
Perrie Edwards, Jesy Nelson, Leigh-Anne Pinnock and Jade Thirlwall formed Little Mix at X Factor's Boot Camp after the judges turned them all down as solo artists.
They became the first ever group to win the reality show this evening after performing covers of En Vogue's 'Don't Let Go (Love)', 'Silent Night' and their winner's single 'Cannonball'.
> X Factor weekly results revealed: Janet Devlin won most often
> Little Mix should win The X Factor 2011, say Digital Spy users