The Twilight star, who has been questioning Agnelli’s motives of taking the actress in, has accused the producer of sleeping with the 22-year-old, the radaronline.com reported.
"Rob knows Agnelli and has been calling him a lot since Kristen has been there," the insider said. "He wants to know why Kristen is staying there ... he is super angry now and has accused Giovanni of sleeping with Kristen, too.
"Giovanni got a call from Pattinson around four this morning, threatening him if he has been sleeping with Kristen," the source said. Love birds Stewart and Pattison split after her affair with her married 'Snow White and the Huntsman' director Rupert Sanders was revealed.