After initial rumours the pair had ended their long distance love over the weekend, Rob has now reportedly accused Rita of seeing other men during their relationship.
Although he didn't name her directly, the Kardashian brother tweeted a series of posts thought to be aimed at the 'R.I.P' singer - and then later deleted them.
He wrote: "She cheated on me with nearly 20 dudes while we were together, I wonder how many she will sleep with now that we apart? But I mean 20?!!!
"How can a woman who is so busy trying to start her own career have time to be with so many dudes all while in a relationship?! I'm actually disgusted a woman could give up her body to more than 20 dudes in less than a year's time while trying to start a career."
Rob's sister Khloe also waded in, tweeting: "Cheaters never prosper @RobKardashian ill be home today... Try and smile little brother". This post was also later deleted.
Rita is still to comment on the allegations, last tweeting to announce her UK tour, 'Radioactive'.