Former UFC fighter Phil Baroni allegedly beat his girlfriend to death in Mexico on Sunday after she admitted to sleeping with another man, according to reports.

Baroni was arrested after he reportedly threw the woman into a shower in a fit of rage, causing her to suffer a fatal head injury.

Officers later found her naked on a bed inside the hotel room, according to Mexican news outlet Tribuna De La Bahia.

The pro fighter reportedly told cops that the couple had gotten into a heated dispute inside a hotel room in San Pancho after his girlfriend, identified only as Paola, admitted she cheated on him, the reports said.

The 46-year-old New York native, who cops believe was under the influence of marijuana and alcohol, told authorities that he then ordered Paola to go bathe, and when she refused to do so he threw her into the shower, the report said.

She hit her head and slipped, then hit her head again when she fell down, he claimed, according to the report.

The former fighter said he then helped her up and into the bed, where he took off her clothes and covered her with a sheet after she told him she was cold.

Baroni claims Paola then asked him to get her cigars and beer, and when he returned she wouldn’t wake up.

He then ran to grab police who were outside the hotel and told them his girlfriend was unresponsive.

Police then found Baroni’s girlfriend, a Mexico City native, naked on the bed and showing “multiple signs of beatings” as well as “no vital signs.”

A full investigation into the incident began following Baroni’s arrest for homicide. He is being held in custody in Valle de Banderas.

A State Department spokesperson confirmed to The Post that Baroni is detained in Mexico and that they are “providing appropriate assistance.”