Robert Pattinson and Kristen Stewart never confirmed when they started dating

An American TV host has caused uproar after comparing Kristen Stewart and Robert Pattinson's relationship to Princess Diana and Prince Charles's doomed marriage.

R-Pattz was being interviewed by New York Times writer David Carr for TimesTalk, a live show in front of a studio audience, to promote his new movie Cosmopolis when conversation turned to the royals.

‘I think America really wants to have a royal family,' said Rob, 26.

To which David replied, ‘So if you and Kristen have trouble it's like Charles and Di having trouble?'

Charles and Diana got hitched in 1981 and divorced in 1996. The Prince of Wales still had deep feelings for Camilla Parker Bowles, who is now his current wife.

The comparison caused booing from the crowd and much embarrassment for Rob.

‘No, I wouldn't really go that far,' he insisted.

It's the latest in a line of awkward interviews for the Twilight star, who has tried to avoid talking about 22-year-old Kristen's affair with film director Rupert Sanders.

The pair were rumoured to be facing their first public meeting since the scandal at the MTV Video Music Awards next month, but the speculation has been quashed after K-Stew was confirmed to appear at the Toronto International Film Festival instead.

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Anna Francis