Aren't they friends? Why is there a feud between Miley Cyrus and Selena Gomez?

A video of Cyrus' concert started to circulate on the internet. It has gone viral not because of her outstanding performance, but because of her unusual performance of her song "FU"

During the performance, Cyrus was seen holding a cardboard cut-out of Gomez in a black bikini while singing the song which had the lyrics: "I don't really have much to say ... I was over it the second that I saw her name ... I got two letters for you ... One of them's F and the other one's U."

Cyrus then proceeded to throwing the cut-out into the crowd.

There is no word yet if there really is a Miley Cyrus-Selena Gomez feud. No one really knows what prompted Cyrus to diss her friend. Gomez' reps have not commented either.

This isn't the first time Cyrus has stirred up controversy with a fellow pop star. She previously fired back at Katy Perry after the two shared a smooch in a concert.

"I just walked up to her to give her like a friendly girly kiss, you know, as girls do," Perry said.

"And then she like tried to move her head and go deeper and I pulled away."

She added, "God knows where that tongue has been...We don't know! That tongue is so infamous!"

To which Cyrus replied: "Girl if ur worried abt where tongues have been good thing ur ex boo is ur EX BOO cause we ALL know where THAT been," she tweeted.

"Dontchyouuuu act like you didn't lurvvvvv it."

What can you say about Cyrus' behavior? Stay tuned to Kpopstarz for more news about the Miley Cyrus Selena Gomez feud!