Spencer Pratt taped an episode of Tyra Banks that will air on April 29 — he swears that a Lauren Conrad sex tape does exist.

Remember when rumors of Lauren Conrad and Jason Wahler’s sex tape first broke… only to quietly go away again?

Spencer Pratt tells Tyra Banks, “I know for 100% fact it did exist – 1000%!”

While Spencer Pratt claims the Lauren Conrad sex video is real, he said he “would never watch that. I would rather throw up… but I know for a fact, and I would take a lie detector test.”

Heidi Montag also appears on the April 29 Tyra Banks (naturally… does Spencer go anywhere without her?) — and her comment about the Lauren Conrad sex tape: “From what I have heard from confirmed sources… her ex-boyfriend was going around trying to sell it… I am really not allowed to elaborate.”