John “Doomsday” Howard once had the privilege of doing what most Bostonians would love to have done.

Howard, a Dorchester native, is scheduled to fight in Sunday’s UFC event at TD Garden. It should be a memorable experience for the local product, but he’ll always remember the time he sparred with Boston Marathon bombing suspect Tamerlan Tsarnaev.

Tsarnaev, an amateur boxer, trained at Howard’s gym in Allston. The two sparred one day, and emotions ran high. According to Howard, Tsarnaev got too cocky, so “Doomsday” took it upon himself to teach his opponent a lesson. He apparently broke Tsarnaev’s nose amid a TKO.

“The sparring happened — it was back and forth — but one day, he got a little touchy, a little cocky,” Howard recently recounted in a interview. “When he did that, the spar got live. And when it got live, we went at it to try to take each other’s head off. But I got the best end of him, and I hit him with a shot to the nose. As he covered up, I hit him to the body and dropped him. A technical knockout, if you want to call it.

“He got humbled that day, definitely.”

Tsarnaev and his brother, Dzhokhar, are accused of carrying out the bombings at the 2013 Boston Marathon. Tamerlan died during the ensuing manhunt when his brother ran over him with a vehicle while fleeing the scene of a shootout with police in Watertown, Mass. Dzhokhar currently is awaiting trial.

Thumbnail photo via Jayne Kamin-Oncea/USA TODAY Sports Images