Simon Cowell’s girlfriend Terri Seymour was left stunned after David Hasselhoff asked her to marry him.

The unexpected proposal happened when the couple were locked in a Las Vegas hotel room as part of a 12-hour reality TV experiment staged by Extra.
 
The 'lockdown' took place in a luxury suite at Planet Hollywood’s Resort and Casino.

The American Idol judge’s long-term lover played videogames and board games with the former Baywatch star, and the pair also enjoyed naked massages together as well as hosting guests including illusionists Penn & Teller and comedian Carrot Top.

But a big surprise came when Seymour realised her roommate, who works for her music mogul boyfriend Cowell on hit show America's Got Talent, asked her to marry him.

The TV experiment, complete with proposal and Seymour's reaction, will air on Extra for three nights, beginning tonight.