DONNY OSMOND’s gun-totin’ son busted by cops and he tells THE ENQUIRER all the shocking details THAT Daddy O doesn’t know!  His son Jeremy was busted for dis­charging a firearm within the city limits of Cedar Hills, Utah, this past summer – and his father didn’t even know about it!

But with The ENQUIRER lifting the lid off Jeremy’s secret, it won’t be long before the famed singer finds out about his son’s arrest. And Donny, who’s currently touring with his sister Marie, isn’t likely to be happy about it.

“Donny’s really going to blow his stack, especially in the wake of the Connecticut school shootings,” a source close to the Osmond family told The ENQUIRER. “Firing a gun irresponsibly isn’t something to just shrug off, like Jeremy seems to be doing.”

Jeremy, a married 31-year-old who got his doctorate in physical therapy last year, was busted on July 21 as he blasted away within city limits.

“I was just target shooting and the police showed up,” Jeremy told The ENQUIRER. “It was right on the border of the city limits and BLM (Bureau of Land Management) property. But I wasn’t arrested.”

When it was pointed out that he was, in fact, arrested and booked for discharging a firearm within the city limits, Jeremy said: “But I was never taken in by police car. There was no actual arrest. I was just issued a citation. I had to go down and have my fingerprints taken, but that was it.”

Jeremy later admitted to The ENQUIRER that he also had his mug shot snapped, yet insisted “it was no big deal.”

He explained that he was practic­ing with a muzzle-loader and there was no one else nearby. “I was about 20 yards from the Wasatch Moun­tains,” said Jeremy, who eventually had to pay a $200 fine. “They let me keep my gun, and I wasn’t charged with illegal possession of a firearm.”

But the close source said: “Even though Jeremy just got a fine, the state of Utah doesn’t take this kind of offense lightly because a civilian could be shot or killed. He wasn’t near any schools or developments, but he was in a recreation area where people could be hiking around. It’s possible the authorities went easy on him because he’s an Osmond, but his dad’s certainly not going to be pleased!

“Hopefully, Jeremy will start to rec­ognize the seriousness of his actions, and the Sandy Hook school-shooting tragedy could be a wake-up call for him.”