BOSTON — A brazen armed robbery erupted in the heart of the Back Bay overnight, where police say a 14-year-old boy terrorized a store clerk with what looked like a Glock before being hunted down just blocks from Copley Square.

The stick-up unfolded around 3:32 a.m. Thursday at 261 Dartmouth Street, when the pint-sized suspect allegedly pointed the fake gun straight at the victim and demanded cash. The clerk, fearing for their life, handed over money from the register as the boy fled into the night.

But the getaway didn’t last long. Officers from District D-4 flooded the streets, blasting out the description and even circulating a photo. Within minutes, eagle-eyed cops spotted the teen strolling down St. James Avenue like nothing happened.

The chase ended at 205 Dartmouth Street, where officers swooped in and slapped the handcuffs on him. Inside his bag? A wad of U.S. cash and the so-called “Glock,” which turned out to be a BB gun.

Police confirmed the teen — just 14 years old — was arrested on the spot. He’s now facing charges of Armed Robbery and Assault with a Dangerous Weapon, with an arraignment expected in Boston Juvenile Court.

Residents are rattled that an armed robbery could unfold steps from one of Boston’s busiest corners — and even more shocked that the suspect is barely high-school age.