Secret Cindy Williams' Took To The Grave: Sitcom Legend 'Torn With Regret' After Rift With 'Laverne & Shirley' Co-Star Penny

Laverne & Shirley icon Cindy Williams spent her final days "torn with regret" years after her behind-the-scenes drama with co-star Penny Marshall, RadarOnline.com has exclusively learned.

Williams portrayed the upbeat Shirley Feeney on the beloved sitcom from 1976 to 1982, offering a comedic punch alongside Marshall, who nailed her role as Laverne DeFazio before going on to become one of the best-known duos on the small screen.

Fans of the beloved show were devastated to hear Williams died after a brief illness on January 30, but a friend said "there wasn't a day gone by Cindy didn't kick herself for leaving the show the way she did and freezing Penny out a long time afterward."

Although it was all laughs as cameras were rolling, reports emerged revealing a rivalry brewing on-set.

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Marshall tried getting Williams to stay upon learning her co-star was expecting, saying, "I don't care, Cin. Lay in bed the whole time and be the biggest pain-in-the-ass pregnant person you've ever seen. I'll run around! Just take care of the dialogue."

Williams said hiding her bump was one of the main concerns on her mind, but the deciding factor was "when it came time for me to sign my contract for that season, they had me working on my due date to have my baby," she told Today in 2015.

She sued for $20 million and the case was settled out of court.

The co-stars later reunited for a 2013 episode of Sam & Cat before Marshall's death in 2018, but Williams "regretting holding a grudge," an insider spilled. "It gnawed at her until the day she died" herself.