The reason Miley Cyrus' parents split up after 17 years of marriage is because mom Tish had an affair with musician Bret Michaels, according to a bombshell report from Us magazine.

According to Us, Billy Ray Cyrus was blindsided by the news and filed for divorce immediately after learning of it on October 27.

Michaels reportedly "became close" to the family earlier this year after he sang a duet with Miley entitled "Nothing to Lose."

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