The 31-year-old actor is believed to have parted ways from his musician girlfriend - and rumoured fiancée - whom he had been dating since 2014, as sources say the pair had begun to "drift apart" in recent months.
An insider told The Sun newspaper: "They were almost inseparable for their first two years together. But in recent months they have really started to drift apart and have been spending less and less time together.
"Rob is tired of it, has called off their engagement and told friends they have split. With so much history between them, though, there are still strong feelings there. It's a difficult situation but things have become tough between them for some time and they both know they were no longer working as a couple."
The report may come as a shock to fans of the couple, as in July the 'Twilight' star seemingly confirmed speculation that he was in fact engaged to the 'Two Weeks' singer, which had been circulating since T-Pain let the news slip in 2015.
When asked if he had popped the question to the 29-year-old beauty, Robert said: "Yeah, kind of."
The 'Remember Me' actor also addressed his somewhat secretive relationship with the singer, as he revealed he keeps his love life under wraps because he's worried about "crazy" fans who believe his romance is a "conspiracy".
He said: "It's one of the most frustrating things in the world, because you want to be able to do that [show PDA], but to get kind of stuck in a position where, like, you have to make the decision ... Do you want to let, kind of, crazy people in, because for whatever reason with 'Twilight', there's like, a crack troop of crazies who think every decision you're making is creating some kind of conspiracy. And so you kind of think, to protect it, I want to create a big boundary between it, but then it makes it difficult for your actual relationship."