Kristen Stewart is "jealous" of FKA twigs.

A source said: "[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.

"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 24-year-old actress is also believed to have called the 'Two Weeks' singer "fugly".

The source continued to HollywoodLife.com: "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."

Meanwhile, another insider has revealed that Kristen is "suspicious"

of FKA twigs - real name Tahliah Debrett Barnett.

A source recently shared: "Kristen was already suspicious of her motives, but when she heard that FKA was straight up talking about Rob to the press, that confirmed it.

"She knows Rob wouldn't be okay with that. It's so obvious to Kristen that this girl is just taking advantage of Rob ... She's still very protective of Rob."

The 26-year-old singer recently admitted that she finds it ''challenging'' being the 28-year-old actor's girlfriend but says it's worth it because she ''loves'' him.

Discussing her popularity with paparazzi, she said: ''I look uncomfortable because I am uncomfortable. But then it's like, is this person in my life worth that? And he is, without question ... In comparison to how happy I am. And how I feel with him. It's 100 percent worth it.

''That side of my life [the paparazzi] is nothing to do with me.

That's, like, that is the ... side of life of the man that I love. And ... when that started happening I had to."