A Gandhi-following, peace-loving, free-spirited vegetarian who was adopted at birth has discovered the worst possible thing a son could find out about his father – his dad is Charles Manson.

“It’s like finding out that Adolf Hitler is your father,” said Matthew Roberts, a Los Angeles disc jockey.

A curious Roberts, 41, began investigating his poisoned family tree about 12 years ago, when he contacted a social services agency, which located his mother, Terry, in Wisconsin, according to the London Sun.

His reluctant natural mom fed him bits and pieces, like his first and middle name — Lawrence Alexander — withholding his infamous surname until she could summon the courage to tell him the truth.

But Roberts pressed her for more details until she finally revealed the shocking secret, that his dad was one of the most infamous serial killers the world has ever known.

“I didn’t want to believe it,” Roberts said. “I was frightened and angry. I’m a peaceful person — trapped in the face of a monster.”

Terry told Roberts he was born after Manson raped her in a drug-fueled orgy in 1967. She gave the baby up for adoption.

Even she admits her long-lost son bears a striking resemblance to the mastermind whose family of commune followers committed nine gruesome murders in Los Angeles in 1969. Their victims included pregnant actress Sharon Tate, film director Roman Polanski’s wife.

Manson, 75, is an inmate at Corcoran State Prison in California.

After five years, Roberts’ eventually wrote to Manson, who replied with letters and postcards — eerily signed with an ugly swastika — the wartime Nazi symbol Manson has tattooed onto his menacing forehead.

Roberts said he has his own bouts with schizophrenia, but other than that, the apple fell far from the tree.

“My hero is Gandhi,” Roberts said. “I’m an extremely non-violent, peaceful person and a vegetarian. I don’t even kill bugs. I’ve had long hair all my life. I could make it go away, but I can’t let the world and their fears change me.”

Two years ago, Roberts said he received a swastika-stamped post card from Manson with a prison phone number, but Roberts never made the call.

“He’s my biological father. I can’t help but have some kind of emotional connection,” Roberts said. “I don’t want to love him, but I don’t want to hate him either.”