"Britney is quite mean, which I think you will discover," said Cowell.
The 52-year-old who is known for giving tough comments himself, says that Spears and fellow judge Demi Lovato are harder to please than him or fourth judge singer L A Reid, reports femalefirst.co.uk.
"They are harder to please than me or L.A. They are very happy giving people a no. They definitely have their own opinions," he said.
SRK-Gauri anniversary: B-Town stars and their non-filmi better halves
Birthday special: Popular mothers and daughters in Bollywood
Spotted: 'Kaabil' star Hrithik Roshan with dad Rakesh Roshan
'Rock On 2' trailer launch: Farhan, Shraddha enthrall audience with live gig
Flashback: When bikini babes set a new world record in Australia