IN a heartbreaking act of tough love, LEONARDO DiCAPRIO has reluctantly washed his hands of his jailbird stepbrother.

Good-guy Leo tried to spark a major Hollywood career for his hot-headed big stepbrother, Adam Farrar, but despite those efforts, the violence-prone thug ended up behind bars after his crime spree.

Now, as DiCaprio’s Christmas blockbuster “The Wolf of Wall Street” hits theaters, The ENQUIRER has uncovered never-before-revealed details about the bighearted actor’s relationship with wayward Adam.

Leonardo and Adam grew up together in Los Angeles after Adam’s mother, Peggy, married Leo’s father, George, when Leonardo was just 1.

“Ironically, it was Adam’s early success in TV commercials and ap­pearances on (the ’70s series) ‘Eight Is Enough’ and ‘Battlestar Galactica’ that piqued Leo’s interest in acting,” a friend said.

“But now Adam has a criminal record and is nearly homeless while Leo is worth more than $200 million.

“Leonardo has tried to help Adam’s acting career, but he was always concerned because of Adam’s hair-trigger personality.”

When DiCaprio’s biggest film, “Titanic,” was released in 1997, Adam was busted for allegedly as­saulting a photographer.

Then, in a real shocker, Adam was accused in 2000 of attempted murder of his then-girlfriend. The case was later dropped, and Leonardo still tried to see the good in him.

“Despite his worldwide success, Leonardo made time to look after his stepbrother, and the pair remained close up until about three years ago,” said the source. The actor even took Adam with him on the party circuit.

But court documents obtained exclusively by The ENQUIRER re­veal that hard-headed Adam just couldn’t stay out of trouble.

In May and June, he was twice arrested for possession of heroin and driving on a suspended license, and he served a brief sentence. Incapable of learning a lesson, the 42-year-old was convicted in Octo­ber of petty theft. After being placed on probation, he violated his parole and an arrest warrant was issued.

Within the last three years, Adam has also been charged with ha­rassment and accused of domestic violence. And, according to court doc­uments filed in 2008, he was ordered to pay child support for his daughter, now 6.

“Leo feels Adam is not only screwing up his own life but also his kid’s life,” said the friend. “Still, when Adam recently got out of prison and there were reports he had gone miss­ing, Leonardo was very upset until he found out that Adam was OK.”

Hopefully, the 39-year-old star’s dose of tough love will finally turn Adam around.

Said the source: “Leo won’t re-enter Adam’s life until he shows for awhile that he can live on the straight and narrow.”