GRAND PRAIRIE, Texas—A birthday party in Grand Prairie ended with the honoree facing a charge of fatally shooting his mother’s boyfriend.

Police said Monday that both men had been drinking.

Police say the party for Christopher Lee Heck, who turns 22 on Tuesday, turned violent when he and 36-year-old Donald Lee Cates got into an argument.

Detective John Brimmer told The Associated Press that Sunday night’s fight began after a married woman at the party sat on Heck’s lap. Brimmer says it appears Cates thought that was disrespectful, the two men argued and Cates slugged Heck in the mouth, breaking his tooth.

Police say Heck went into the house, got a pistol and shot the unarmed Cates.

A statement from police says Heck was located walking nearby and arrested. He remained jailed Monday, facing a murder charge. Brimmer said there was no information yet on Heck having an attorney. Grand Prairie police say a handgun was recovered at the scene.