Republican presidential hopeful Marco Rubio is hiding a bombshell drug scandal that could derail his bid for the Oval Office — an ex-con relative with ties to a major cocaine-smuggling operation!

Brother-in-law Orlando Cicilia, married to Rubio’s older sister Barbara, was a key player in the so-called “Cocaine Cowboys” era of 1970s and 1980s Miami.

He was busted on racketeering charges in 1987 for his involvement in a ring that sold millions of dollars worth of drugs, sources say!

And now ‚ a week after The National ENQUIRER first broke the story, the Washington Post has revealed that Rubio even sent the Florida Division of Real Estate a letter in 2002 — on official government stationary — that recommended Cicilia for “licensure without reservation.”

“This is political dynamite that could blow up Rubio’s campaign — it’s the last thing he needs to come out!” a political insider told The National ENQUIRER.

Cicilia, 58, was convicted in 1989 and was released in 2000 after serving 12 years. In his book “An American Son,” Rubio — who was 16 at the time of Cicilia’s arrest — admitted that his in-law was involved in a “criminal enterprise.”

But he never mentions Cicilia fronted coke kingpin Mario Tabraue’s operations out of a Miami exotic animal business!

“Mario was the kingpin, and Orlando was his second in command,” former detective Michael Fisten said.

“He always had large amounts of cash on him.”

Cicilia insulated Tabraue by handing Colombian coke off to buyers and directing drug shipments around the country, an insider added.

While there’s no evidence Rubio knew of Cicilia’s drug smuggling, the ties between the two could be damaging — as evidenced by a photo catching the ex-con on the podium of the Biltmore Hotel at Coral Gables, Fla., as Rubio made a victory speech after winning his 2010 Senate seat.

Not to mention that young Rubio received money from his brother-in-law for various tasks, including washing his dogs and building animal cages.

And, a source said, Cicilia’s sons, Daniel and Landy, have gotten more than $130,000 working for Rubio-affiliated PACs and campaigns!

“It’s nice that Marco is loyal to his family,” the spy warned, “but he better move to distance himself from his brother-in-law before his association with Cicilia crashes his campaign!”