Actress Kristen Stewart is reportedly jealous of FKA twigs, who is dating her ex-boyfriend Robert Pattinson.

According to a source, the 24-year-old, who split from her `Twilight` co-star after she had an affair with Rupert Sanders, has slammed Pattinson's new romance, reports hollywoodlife.com.

`(Kristen) is convinced this is just a fling. (FKA twigs) will grow tired of Rob within half-a-year. Kristen just can't see the relationship lasting,` the source said.

`In a conversation with close friends at a recent party in Silverlake, Los Angeles, Kristen dissed Twigs' looks."

`Kristen has become very jealous of Rob's new romance,` the source added.

Stewart is also believed to have called FKA twigs' fugly.

The source said: `She was being really hard on Twigs' looks, calling her fugly. She even commented that Rob can't be dating her because of her looks.`