Mariska Hargitay is making headlines not for her Emmy-winning role on Law & Order: SVU, but for a deeply personal revelation in her new documentary My Mom Jayne which premiered at Cannes Film Festival.

The film, a tribute to her late mother, Hollywood icon Jayne Mansfield, also includes a jaw-dropping secret Mariska has kept hidden for three decades: Mickey Hargitay, the man who raised her and whom the world believed to be her father, is not her biological dad.

Hargitay revealed that her biological father is Nelson Sardelli, a Brazilian-born entertainer and former Las Vegas headliner who was romantically linked to Mansfield during the 1960s.

In an interview with Vanity Fair, Hargitay recounted that in her 20s, someone showed her a photo of Sardelli and she immediately knew in her bones that he was her biological father. But when she confronted Mickey, he denied it.

When she was 30, Hargitay went to see Sardelli perform in Atlantic City and when she introduced herself, he burst into tears, telling her, “I’ve been waiting 30 years for this moment.”

The documentary explores not just the glamour and tragedy of Mansfield’s life, but also the personal journey Mariska undertook to uncover and accept her own lineage. Sardelli, now in his late 80s, gave his blessing for the revelation, and appears in the film, along with his other two daughters – Mariska’s half sisters.

Also featured in the documentary are Mariska’s sister, Jayne Marie Mansfield, and brother, Tony Cimber, from her mother’s first and third marriages.