The Hills star Spencer Pratt has been caught lying about his girlfriend Heidi Montag's purity - he insists she's still a virgin.

Pratt was promoting the new season of the reality TV phenomenon on Los Angeles Ryan Seacrest's morning show, when he cooed about Montag's no-sex-before-marriage promise.

He told the radio host, "She's still a virgin... We don't sin over here," adding that he and Montag place pillows between them in bed at night - to help them fight temptation."

The reality TV star went on to state his girlfriend is so religious, she's considering recording a Christian album for a quickie interview.

But website HollyScoop.com have unearthed footage from the first season of The Hills, when Montag has a heart-to-heart chat with Pratt after taking a pregnancy test.

The website asks, "Last we checked, if you're a virgin, you wouldn't need to take a pregnancy test."