The Sons of Anarchy star was a 20-year-old employee at a Los Angeles restaurant when she served Simmons following the band's concert at the Santa Monica Civic Auditorium in the mid-1970s.
Sagal, who was an aspiring singer at the time, performed for the rocker, flirted with him, and went home with Simmons.
"He was quite persuasive, and I like men," she writes in her memoir Grace Notes.
Simmons accompanied her to her band practice the next day and introduced her to the president of his record label, Neil Bogart, who signed her group. However, her big break never came to fruition after the band's first album sold poorly and they were released from their contract.
Sagal maintained her relationship with Simmons even though she knew he wasn't a one-woman guy.
"I fantasized that I would be the exception," she continues.
The relationship eventually came to an end after another musician proposed to Sagal. She reportedly told Simmons about the engagement and informed him she would decline the marriage offer if the Kiss star wanted to wed her, but he reportedly laughed.
In her memoir, which is due out next month (Mar17), Sagal also opens up about her career change from music to acting, her drug abuse, a battle with cancer and her three marriages.
She's still looking for a big music break and is currently performing with the band The Reluctant Apostles, which features musicians who tour and record with Elvis Costello and Tori Amos.
"We formed this band because I just wanted to be in the band," she tells WENN. "I didn't want it to be my name. I'm the girl singer. I love it. I play tambourine, I play bongos, I sing a lot, lots of harmonies... We just really love to play. We have some original and some really obscure covers."
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