Kaitlynn Carter's relationship with Miley Cyrus started while she was still dating Brody Jenner, according to Spencer Pratt.

In an episode of the rebooted reality show The Hills: New Beginnings on Monday, Kaitlynn, who was still in a relationship with Brody at the time of filming, hit back at rumours that the pair had an "open relationship".

Since her split from Brody, Kaitlynn has been seen on numerous occasions getting close to Miley, but Spencer alleged in a piece for Cosmopolitan magazine that the pair's "relationship" started while she was still with Brody.

"It’s tough for me to listen to Kaitlynn complain about people talking about her allegedly open relationship with Brody when we know she had a thing going with Miley,” he said. “She already had something going on with her when these scenes were filming — maybe not physically, but definitely emotionally. No one’s judging you for whatever it is you and Brody do when he’s not sleeping in his car. We just don’t want people to lie about their lives."

It was also speculated that Kaitlynn and Miley's rumoured romance was responsible for the singer/actress' split from husband Liam Hemsworth, but the Wrecking Ball star furiously hit back at those allegations in a string of angry tweets in which she insisted she had never cheated on her spouse.