Collins -- who is in the middle of a nasty, prolonged divorce with actress Faye Grant -- revealed to her in 2012 he had molested and/or exposed himself to several underage girls years before. Collins and Grant went to a therapist where she peppered him with questions about the incidents ... and he not only answered, he was specific.

Here's what Collins didn't know at the time. Grant taped the therapy session. We're told her lawyer advised her it was legal to secretly record the conversation because in California you're allowed to secretly record conversations to gather evidence the other person committed a violent felony ... and molesting a child under the age of 14 qualifies.

We have protected the names of the victims Collins mentions on tape. As you listen ... you will hear Collins refer to a "disclosure" and a "list." This refers to a confession Collins had already made to his wife ... which triggered the therapy session.

You hear Collins flatly confess to molesting an 11-year-old New York girl -- a relative of his first wife -- saying, "There was one moment of touching where her hand, I put her hand on my penis." He also acknowledges exposing himself to the girl "a couple of times" ... he says when she was 11, 12 and 13.

We're told the woman says in the '90s she was watching TV with her husband and saw Collins on the screen, and then told her husband for the first time Collins had molested her.

We're also told in 2000 the woman contacted Collins' current wife, Faye Grant, by sending her an anonymous letter warning her that her husband was a child molester.

Nothing happened for 12 years. Then, in late 2011 ... Grant reached out to the woman, after Collins told his wife about the sexual contact, and the girls with whom it had occurred with.

Grant sent the woman an email -- obtained by TMZ -- in which she says, "Stephen lied when confronted 12 years ago. He said he had a hole in his holey jeans, as was the style then, and you 'must have' seen his genitalia one time."

Grant goes on, "Stephen is not remorseful, shows no guilt, and his shame is demonstrated as extreme self pity. He wails and cries, 'I'm in so much paaaaaain!!!'"

He wails and cries, 'I'm in so much paaaaaain!!!'"