Renato Seabra, 21, of Cantanhede, Portugal, was arrested and charged with second-degree murder in the death of 65-year-old Carlos Castro, said New York Police Department spokesman Sgt. Carlos Nieves.
Castro was found dead on Friday in a room of the InterContinental New York Times Square hotel that the two men had shared.
Friends in New York said they were a couple. But Seabra's mother told Portugal's TVIndependente television network that her son "was not Carlos Castro's lover."
Seabra "never hid his sexuality: that he is heterosexual," Odilia Pereirinha said Sunday before heading to New York.
Portugal's Lusa news agency said Monday that Portuguese officials would meet with Seabra.
Seabra was detained by police on Saturday after he sought care at St. Luke's Roosevelt Hospital, not far from the hotel. Police said he was at Bellevue Hospital Center on Monday, where he was undergoing psychiatric evaluation.
It was not immediately known if he had retained a lawyer.
Castro and Seabra had arrived in the U.S. in late December to see some Broadway shows and spend New Year's Eve in Times Square, according to a family friend.
There had been some friction between the two men toward the end of the trip, but nothing to suggest that anything horrible was about to happen, said the friend, Luis Pires, the editor of the Portuguese language newspaper Luso-Americano.
"I think that they were a little bit upset with each other, for jealousy reasons," Pires told The Associated Press.
Seabra was a contestant last year on a Portuguese TV show called "A Procura Do Sonho," or "Pursuit of a Dream," which hunts for modeling talent.
He didn't win the show but did get a modeling contract with an agency founded by fashion designer Fatima Lopes, who developed the show and was a judge on it.
Police said the victim suffered serious head trauma. The medical examiner's office will determine the cause of death.