WTF! BRET MICHAELS HAD AN AFFAIR WITH MILEY CYRUS MOM!

Is Bret Michaels the reason for Billy Ray Cyrus' Achy Breaky Heart?
That depends on who you ask.

Billy Ray and wife Tish called it quits last week after 17 years of marriage, with the parents of teen star Miley filing for divorce on Oct. 27.

Though the court papers cited irreconcilable differences, Us Weekly reports Tish and rocker Michaels had an affair earlier this year that led to the breakup of her marriage.

Michaels, who has been in an on-and-off relationship with his baby mama, Kristi Lynn Gibson, allegedly got close with Tish after he collaborated with Miley on the song "Nothing To Lose" in February.

Tish, 43, and Michaels, 47, reportedly developed a romance soon after.

"Billy Ray was completely unaware of what was going on," a source told Us, adding that once Billy Ray found out, he filed for divorce. Billy Ray also allegedly found out Tish had another affair as well.

But reps for both Michaels and Tish are slamming the report, with the Poison frontman's team saying, "There has never been an affair or a fling."

Still, the mag's source is adamant that there "was a professional relationship that turned into something more."

In announcing their split, the Cyruses released a statement saying, "As you can imagine, this is a very difficult time for our family. We are trying to work through some personal matters. We appreciate your thoughts and prayers."

Billy Ray is seeking joint custody of the couple's five children.