Credit: Steven Lawton/FilmMagic; Michael Bezjian/WireImage.com

A new twist in the Speidi sex tape saga: Spencer Pratt claims he has footage of his ex Heidi Montag getting it on with her pal, Playboy Playmate Karissa Shannon.

Pratt, 26, tells TMZ.com he was picking up some of his belongings from the Malibu pad he once shared with Montag, 23, when he found the X-rated footage.

Shannon, 20, tells TMZ a tape exists, but she doesn't believe Pratt has a copy.

This is now the third tape that has allegedly surfaced featuring The Hills star. The first two supposedly star Pratt. One features a pre-surgery Montag; the other was filmed after she underwent her infamous 10 cosmetic surgery operations last year.

Over the weekend, Pratt and Montag got into a cussing fight - via Twitter - over the tapes.

In July, Montag filed for divorce after one year of marriage, citing irreconcilable differences. Their divorce is expected to be finalized on Valentine's Day of next year.