Robert Pattinson thinks Kristen Stewart looks like "an alien".

The 25-year-old heartthrob - who is dating his 'Twilight' co-star, who plays Bella Swan in the vampire franchise - admitted in scenes from 'Breaking Dawn', in which Kristen's alter-ego's baby eats her from inside, he was shocked by how "thin and ghastly" she looks.

He told Premiere magazine: "There are scenes were Bella looks like an alien. When the baby eats her from inside, she looks so thin and ghastly.

"Kristen had to wear this horrible makeup and when I'd see her come on set, I'd ask the crew, 'Are you sure we're filming 'Twilight'? Isn't it supposed to be harmless and PG-13?'"

Despite Robert's concern over his girlfriend's shocking look in the latest 'Twilight' movie, Kristen recently admitted she "loves" playing a vampire.

She said: "I f***ing love being a vampire. I was 17 when I read 'Twilight,' and at the time it was so perfect for me.

"The script was about young kids who think they can handle stuff that they just can't. And they're going to do it anyway. Because, why not? Just torture yourself. I relate to that. Vampires are a little dangerous - and we girls like to test ourselves."