Kristen Stewart allegedly had an affair with movie producer Rupert Sanders while she was dating Robert Pattinson, but it appears that her boyfriend at the time may also have been guilty of infidelity.

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On Wednesday, Radar Online reported that the former Twilight couple were supposedly in an open relationship, which apparently caused problems between them.

"When they were officially dating, they always had a policy of 100 percent honesty, which did create issues," a source revealed. "Robert was always very frank about his flings with other women and that worked for Kristen too."

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Not only did the exes reportedly sleep with other people, but Stewart might be bisexual, according to the insider.

"They had an open relationship and it's amazing that Kristen hasn't revealed this info when she was being painted as a 'jezebel,'" the source continued. "Rob has had other women on the side and Kristen has had other women and men as well."

It also looks like the relationship between Stewart and Pattinson wasn't a typical romantic partnership, but more of a business deal.

"Rob and Kristen often said they might never see each other again after the last Twilight press tour and that's pretty much what happened, except for their 'are you in town' booty calls," the source said.

As for where their relationship currently stands, the source mentioned that the former couple still keep in contact, and are supposedly hooking up when the opportunity comes along.

Stewart worked with Sanders in Snow White and the Huntsman where the two were rumored to have had a fling.

Tags: Kristen Stewart Robert Pattinson