DETROIT -

The public breakup between "Twilight" stars Kristen Stewart and Robert Pattinson is about to get uglier, according to several online entertainment sources.  That's because the two stars are locked in a bitter custody dispute over their dog.

The couple adopted Bear together from a shelter in New Orleans but after Stewart was discovered cheating on Pattinson with her 'Snow White And The Huntsman' director Rupert Sanders, Pattinson moved out of their Los Angeles home.

A source told RadarOnline: "After Rob moved his things out of their Los Angeles apartment, he then told Kristen he wanted Bear. She was heartbroken - they adopted Bear together and she always felt that he was their little baby. But Rob was so hurt by Kristen's actions he decided that he wants the dog to help him get over what happened. After all, a dog is a man's best friend and Bear is such a good companion.

However, Kristen won't give up Bear in a hurry. She helped Rob save Bear from Parvo disease [a highly contagious disease which causes death in 91 per cent of cases when left untreated], which nearly took its life when it was a puppy. She wants joint custody - and it could get a little messy."