The pop star eased the pain of her split from John Mayer by spending time with her long-term pals Rob and his on-off girlfriend Kristen Stewart last month.

But during one karaoke party Kristen allegedly got the shock of her life when Katy confessed she'd love to date Rob should they split up again.

According to Star magazine “Kristen looked like she wanted to run away” after Katy's comments.

She was then said to have questioned Rob whether “rumours of them hooking up in the past are true”.

Kristen and Rob are currently back ON after a rocky nine months following the beauty's fling with married movie director Rupert Sanders.