Britney Spears and Heidi Montag have denied involvement in a duet featuring the pair that surfaced this week.

American Idol host Ryan Seacrest admitted he had no idea where the track – called Dramatic – came from when he debuted it on his breakfast radio show on Monday.

He said: "I just opened an email and there was this track and it said, 'Britney Spears and Heidi Montag'."

After previewing the demo, the DJ added: "How can you do that? If she doesn't know Britney, how can she (Montag) do a song with Britney? You've gotta get a little Britney permission on that I would think."
 
Meanwhile, a source at Britney's record label, Jive, tells Usmagazine.com: "It’s not authorized and it wasn’t set up in any way and they never spent any time together in the studio. This was never a planned song or duet in any way."

And a rep for pop-wannabe Heidi – the most likely candidate for the ‘leak’ – insists: "Heidi has no knowledge of this recording. She did do a demo of this song for possible use on her record, but that recording had a male vocal on it, not Britney Spears."

The mystery deepens...