Justin Bieber cheated on Selena Gomez with Rihanna?

The teen idol is said to have had an affair at the beginning of their relationship with the 'Umbrella' hitmaker Rihanna, reported Radar online.

"It has devastated her," a friend of Gomez and Bieber said.

The source alleges that 18-year-old Bieber got together with Rihanna after flirting with each other at a basketball game in Los Angeles back in February 2011.

"It really cut like a knife because it happened in February of 2011, when Selena and Justin had been dating for months and were falling in love," the friend said.

"It's caused Selena to question their entire relationship. Selena thinks maybe they've been hooking up all along," the friend added.

Bieber and Gomez started dating in late 2010, but have split up on more than one occasion in recent months.