Robert Pattinson and Kristen Stewart Fight Over Dog

After discovering his girlfriend's affair, Rob Pattinson has reportedly separated from Kristen Stewart and is fighting to keep their dog, Bear.

It is a battle often fought by exes, and although they do not have children, both Stewart and Pattinson feel very close to their once-shared pet.

Along with feeling "angry, hurt, and upset and sick and tired of people taking sides" following news of Stewart's cheating, as the Daily Star reported, Pattinson is embroiled in a bitter custody battle with the actress over Bear.

Co-stars in the hit "Twilight" films, Stewart and Pattinson were in a serious 4-year relationship where the British actor was rumored to have plans to marry Stewart.

Pattinson, 26, moved out of the Los Angeles home he shared with Stewart last week following her public apology for having an affair with director Rupert Sanders. Sanders, 41, directed Stewart's latest film, "Snow White and the Hunstman." His wife, Liberty Ross, was Stewart's co-star in the film.

"After Rob moved his things out of their Los Angeles apartment, he then told Kristen he wanted Bear," a source close to the actors told

"She was heartbroken- they adopted Bear together and she always felt that he was their little baby," the insider continued.

Meanwhile, Pattinson has not commented on his current relationship with Stewart. The actor is reportedly taking time away from the actress.

"Rob was so hurt by Kristen's actions he decided that he wants the dog to help him get over what happened," to source noted, as reported by "After all, a dog is a man's best friend and Bear is such a good companion."

Stewart, 22, will not give up the canine though, and wants joint custody, according to the insider.

"It could get a little messy," said the source.

In an attempt to save her relationship with the British actor, Stewart released a statement last week: "I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected. This momentary indiscretion has jeopardized the most important thing in my life, the person I love and respect most, Rob."

"I love him, I love him, I'm so sorry," the actress concluded.