(Cover) - EN Showbiz - Robert Pattinson reportedly became high-strung when a sexy photo shoot went "too far."

The actor is currently in a committed relationship with his Twilight franchise co-star Kristen Stewart.

Robert didn't allow himself to get too excited in the presence of nude models while shooting an editorial for French Premiere magazine.

"Rob was asked to pose bare-chested with a sexy blonde model, who happened to be topless as well," a source told Radar Online. "He did his best Blue Steel for the camera as the girl snaked all over his body, nibbling his earlobes, kissing his face and neck and pressing her bare boobs against him, but you could see he was uncomfortable with it."

"Rob was really torn -- because the girl was stunning and he's a bit of a cad -- he was definitely having a really good time being half naked with a hot blonde but then he seemed to get all nervous and started worrying that it was just going too far."

When photographers wanted to heighten the sexiness, Rob declined.

"Toward the end of the shot the photographer instructed the model to lick Rob's nipples!" the source detailed. "That was the kiss of death -- Rob called cut and went in his dressing room and made a phone call." (C) Cover Media