Nikki Reed found watching her Twilight co-stars' relationships fall apart "very, very sad".

The actress portrays Rosalie Hale in the movie series, and is currently promoting the penultimate instalment called Breaking Dawn Part 1.

The franchise also stars Kristen Stewart, Robert Pattinson, Ashley Greene, Taylor Lautner and Kellan Lutz. Nikki has revealed several of her co-stars no longer get on, but she refused to name them.

"It was very, very sad. Let's just leave it at that," she said. "Attachments grow when you're working with the same people for so long. People are friends, people fall in love, people get in fights. We're not all robots in that way. Sure, things have gone on, and it's weird to have them be in the public eye."

The 23-year-old star loved being part of the vampire films at the start. She made a lot of friends, but as time went on the atmosphere changed.

"In the beginning, it was innocent and fun, and we were like one big happy family. It was like being at sleepaway camp," she told the December edition of Seventeen magazine.

"Success came along and changed the dynamic. We're not all best friends, and we're not all going to hang out together after the final movie is done."

Nikki hit the big time after appearing in the 2003 movie Thirteen alongside Evan Rachel Wood. It covered topics such as under-age sex and drug taking and changed the way people viewed Nikki.

"I got typecast as a party girl when Thirteen first came out. The funny thing was, I was a virgin, I didn't do drugs, and I barely drank," she explained.

Breaking Dawn - Part 1 premiered in Los Angeles last night, with Taylor keen to discuss his future plans. He enjoyed working with Kristen and Robert so much he's already thinking about collaborating with them again.

"If I did a film again with them, I'd like to do a comedy. A super, super funny movie," he laughed. "I think they're funny, especially when they're together. Our relationships together are quite hilarious, so it would be a funny movie, for sure."