One person who isn't amused by Jonah Hill: Rob Kardashian. A source tells Us Weekly that Kardashian, 25, dumped singer Rita Ora because he learned she had hooked up with the actor!

"Rita spent the night with Jonah during a trip to New York," the insider says of the British "How We Do" singer and the newly-single Moneyball actor, 29. Find out how Kardashian discovered Ora's betrayal (after nearly a year of on-and-off dating) in this week's Hot Stuff video, as explained by Us Weekly Senior Editor Ian Drew and special guest, reality star Nyasha Zimucha, who's now launch a new website,

Also in the roundup? More on pregnant Duchess Kate's holiday plans with Queen Elizabeth -- who invited her parents in a royal first; how Melissa Gorga's new book deal will get Teresa Giudice's goat; details on Christina Aguilera's 32nd birthday bash, and more!

Watch the video now.