A man who police said spent months harassing and stalking his ex-girlfriend pleaded guilty Monday to killing her new boyfriend.

Matthew Anthony Lambert, 24, pleaded guilty to third-degree murder, conspiracy, reckless endangerment and stalking.

He will be sentenced by Allegheny County Common Pleas Judge Edward J. Borkowski on Jan. 11.

Police said Lambert killed Tre Valorie on May 8, 2019, after following Valorie and his ex-girlfriend from bar to bar that night.

The woman told police that she and Valorie had gone to Tramp’s Bar on Greentree Road, when Lambert walked in and asked to see Valorie outside.

When Valorie returned to the bar, he told his girlfriend that “Matt just told me he was going to pay someone to shoot me,” the complaint said.

The couple left and went to Rumerz on the North Side, and Lambert followed them, police said.

It was when the couple left Rumerz, the complaint continued, that Lambert shot Valorie as he drove home.

He died from a gunshot wound to the head.

Police said surveillance footage near the bar captured the shooting — showing Lambert circling the block and waiting for the couple.

Further investigation, police said, revealed hundreds of text messages from Lambert to his ex-girlfriend, in which he threatened her, as well as any man she was with.

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