Miley Cyrus supposedly “feels betrayed” by Katy Perry.

The pop stars engaged in a saucy Twitter exchange on Thursday which was prompted by statements the Prism singer made about a kiss they shared at one of Miley’s concerts late last month.

Katy described her peer’s tongue as “infamous” during a TV appearance this week, and Miley purportedly considered the comment a stab in the back.

“Miley thought it was really uncool of Katy to talk about their kiss like it was such a gross thing. It’s not like Katy is some innocent angel. Miley is just like, ‘Why are you insulting me?’” a source told Hollywood Life.

“She doesn’t understand why Katy felt the need to put her down when she was on Australian TV. Miley feels betrayed, she thought they were tight and apparently they aren’t.”

Miley tweeted Katy first yesterday, writing: “Girl if ur worried abt where tongues have been good thing ur ex boo is ur EX BOO cause we ALL know where THAT [tongue] been (sic).”

The 21-year-old boldly referred to the Roar singer’s rumoured ex-boyfriend John Mayer, who is notorious for being a lothario in the past, in what appears to be a veiled jibe.

And it is claimed Miley felt the need to bring John into the equation because she has been a pillar of support for Katy throughout their alleged split.

“She was there for Katy during her breakup with John and now Katy is just being mean-spirited and rude, and acting like she’s better than Miley,” the insider said.

While appearing on Australian show Sunrise, Katy said she was stunned to receive the front row smooch from Miley.

“I just walked up to her to give her like a friendly girly kiss, you know, as girls do, and then she like tried to move her head and go deeper and I pulled away,” Katy recalled.

“God knows where that tongue has been. We don't know! That tongue is so infamous!”