Shocking story of how Jack Nicholson discovered his sister was actually his mother

Jack Nicholson has a complicated family tree which he himself only came to learn of after almost 40 years.

The 88-year-old veteran movie star believed for decades that his biological mom, June, was his sister and that his grandmother, Ethel May, was his mom.

As confusing as it sounds, it makes sense when you consider Ethel May was trying to protect her daughter from the supposed 'shame' of having a pregnancy out of wedlock, which was rampant around the time of Nicholson's birth.

It all started when June became pregnant in 1936 to a man, Don, who was married to another woman and Ethel May ordered him to stay away from her pregnant teenage daughter.

The star only found out about his real birth mom when he was almost 40 (Kevork Djansezian/Getty Images)

When the 18-year-old gave birth to Nicholson, Ethel May raised her grandson as her own and the family went on to pretend June was his big sister.

When Nicholson turned four, June relocated to Miami to become an Earl Carroll showgirl. When a young Nicholson decided to pursue his own career in Hollywood at 17 years old, he headed to Los Angeles to join his 'sister' June.

It was only in 1974 when his noir thriller Chinatown was preparing to hit theatres that he came to learn of family history as journalists contacted him to clarify some confusing details.

Time magazine had hit a profile on the then 37-year-old who had starred in 15 movies throughout the 1970s and later bagged an Oscar for One Flew Over the Cuckoo’s Nest.

Jack Nicholson in the 1970s (Roy Jones/Getty Images)

But before they published, researchers contacted Nicholson and informed him they felt his father was alive, living in Ocean Grove in New Jersey, and that his mom was his grandma and his sister was actually his mom.

Nicholson reportedly asked the magazine to hold back on publishing the details while he searched for the truth himself.

According to Patrick McGilligan’s biography Jack's Life, Nicholson then phoned a close relative and told him it was the 'most f***ed up thing I've ever heard'.

“A guy calls me on the phone, and says that my father is still alive, and that Ethel May wasn’t really my mother, that June was my mother,” he reportedly said.

His grandma and mom had already died before he could confront them with the truth (Ralph Dominguez/MediaPunch via Getty Images)

The relative initially denied it until Lorraine, Nicholson's aunt, who he thought was another sister, confirmed it all.

Sadly, both Ethel May and June had died by the time he found out.

And although The Shining star was robbed of the chance to confront the pair or seek some kind of closure about it all, he told Rolling Stone that he didn't really find it 'traumatic'.

“It wasn't what I'd called traumatizing,” he said, instead saying it was 'dramatic'.

“I was very impressed by their ability to keep the secret, if nothing else. It’s done great things for me.”