BACHELORETTE contestant Dylan Petitt is hiding a heartbreaking secret from gorgeous Andi Dorfman…

 – his two siblings both died from drug overdoses.

While Dylan was open about losing his brother and sister in his ABC bio, there was no men­tion of drugs. And that may not sit well with this season’s “Bach­elorette.” When brunette beauty Andi, 27, isn’t looking for love on reality TV, she’s putting away criminals as an Assistant District Attorney in Atlanta.

Dylan’s younger brother, Patrick, 23, died on Nov. 12, 2013, from “opiate intoxi­cation/substance abuse,” according to his death certifi­cate. A friend of Dylan says the 26-year-old Boston accountant still hasn’t recovered from the trag­ic loss.

“It hit him like a ton of bricks when he got the news,” the friend divulged.

IN an EXCLUSIVE INTERVIEW with The ENQUIRER, Dylan’s mom, Diane, explained that, as his big brother, Dylan felt responsible for Patrick.

“When Patrick suddenly died, it sent Dylan into a tailspin,”

 said Diane. “He’s still dealing with it, but be­ing on ‘The Bachelorette’ was a good distraction for him.”

Dylan started filming the show earlier this spring, just a few short months after Patrick’s death.

It was the family’s second drug-related tragedy. According to the friend, Dylan’s sis­ter “got caught up with the wrong guy” and was on probation for felony drug charges when she died on Dec. 8, 2009, after ingesting a combination of ethanol, co­caine and oxycodone. She was 34.

“If Andi does end up picking Dylan, he’s going to have a lot of explaining to do,” said the pal. “She usually prosecutes people who use illegal drugs – not marry their family mem­bers.”