Famed actress Hedy Lamarr – who made movie history with her nude swimming scene in “Ecstasy” – deceived her eldest son all the way to the grave, insisting he had been adopted, new evidence suggests.

But James Loder, whom Lamarr booted from her home when he was a young boy, is actually the star’s natural son, an investigation in the March issue of Talk magazine says.

The Austrian-born Lamarr died in January 2000 at the age of 85 at her home in Orlando, Fla.

She left between $1 million and $2 million to her two younger kids – Denise and Tony – but cut Loder out of her will completely.

Lamarr had always referred to James as her adopted child, and when he was 11, she shipped him off to boarding school and seemed to wash her hands of him.

“The last I saw of my mother as a child would have been when I was about in fifth grade. I tried to write to her, but the letters were returned,” Loder, now 61, tells Talk.

“Effectively, she just said, ‘You’re no longer my son. Goodbye.'”

But Loder always felt there was more to his birth than he knew.

And that hunch was confirmed when he recently tracked down a copy of his birth certificate, which shows he was born as James Lamarr Loder, the magazine says.

At the time, Lamarr was wed to Gene Markey, but the father was listed as John Loder, who would marry her four years later.

James Loder’s kid sister, Denise, tells the mag that Lamarr thought of James as troublesome.

“I don’t think my mother could deal with it . . . [but] I don’t know how she could have given him up. I would die before I’d give up a child,” she says.

The mag says Loder has apparently settled with his mom’s estate for about $50,000 – less than some of the bequests made in the will to people to whom she was not related.