A 77-year-old, Irish-born man with dementia has died at a Brooklyn hospital after another patient, an ex-con and fellow dementia patient, sucker punched him for accidentally walking into his room.

NY Daily News reports that Patrick Sheehan passed away five days after Larry Hammond, 65, attacked him inside the Kingsbrook Jewish Medical Center in East Flatbush on Oct. 22. Mr. Sheehan was born in Cork City, Cork, Ireland and immigrated to Boston, Massachusetts before settling in Gerritsen Beach/Marine Park, Brooklyn where he married his wife Alice.

"They said that my husband went down the hall and he went into the wrong room,” said Sheehan’s wife. “When Pat walked in, (Hammond) just shoved him out. He punched him ... and he stomped on his head when he was down."

NYPD Chief of Detectives Robert Boyce said Hammond punched Sheehan “from behind,” and Sheehan fell and hit his head.

“There was no argument that precipitated the assault,” Boyce said. “(It’s) a sad story.”

Police said that the hospital did not call them until a day after the attack.

Alice Sheehan also wasn’t notified about her husband’s attack until eight hours after it occurred. By the time she heard and rushed over to the hospital, it was too late.

“When I got there, he was comatose,” said Sheehan.

Alice Sheehan’s sister Anne Connaghan said the nurses at Kingsbrook enjoyed caring for her brother-in-law, who had just moved into the hospital on Oct. 5 while his family looked for a nursing home.

"They all loved him because he was so easygoing,” she said. “A couple of the nurses had said 'I wish he was my grandfather.’"

An autopsy will be conducted to see if Sheehan died from the blow to the head.

Police charged Hammond with assault, menacing and harassment.

A judge ordered him held without bail during a brief arraignment on Oct. 28 in Brooklyn Criminal Court, and charges are expected to be upgraded once the case is handed to the grand jury, NY Daily News reports.

According to police and court records, Hammond has a history of violence. He has done five stints in state prison for robbery and attempted robbery since 1972, but hasn’t been arrested or incarcerated since 1997.

A dementia patient was murdered by a fellow patient after walking into the wrong room at a Brooklyn hospital.iStock/Getty Images