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."