Britney Spears was so scared she used expletives during an X Factor US audition.

The pop princess apparently couldn't help using foul language after being startled by unexpected noise from a storm.

Britney was watching one of the contestants audition on the singing contest when the performance was interrupted by a loud booming that rocked the auditorium. This caused the mother-of-two to go into panic mode and she started swearing, screaming and inadvertently spitting on fellow judge Demi Lovato.

'Oh my God,' Britney yelled. 'That was f**king scary as sh*t. We need to get out of here.'

In the episode that aired last night in the US, the family friendly show tried to cover up Britney''s cursing. Producers chose to sound out the star''s swearing which has been heralded as her realest moment on the show so far. Britney took to her Twitter page to apologise to her followers her might have been offended by her potty-mouth.

"Pardon my french there, but I hope u all enjoyed that! Back in a bit to tweet with the West Coast. Xo,(sic)" Britney tweeted earlier today.