Gardaí believe a man fatally assaulted at Cork's Mercy University Hospital (MUH) in the early hours of this morning did not know his alleged attacker.
The man has been named locally as 89 year old Matthew Healy from Berrings, Co Cork.
His wife Delia died earlier in January. He is survived by two sons, and one daughter and predeceased by another daughter.
A man in his 30s from the North side of Cork city is in custody and a major garda investigation into the matter is now underway.
The incident occurred in a ward in the main block of the city centre hospital at around 5.30am.
The exact details of what happened are still under investigation but it is understood that an inpatient in his 80s, who was in a ward of the hospital, was apparently attacked by another inpatient some time before 5am.
A number of people, including a handful other hospital patients, are understood to have been in the ward when the assault took place.
Medical staff raised the alarm and immediate and frantic efforts were made to resuscitate the elderly man but they were unsuccessful and he was pronounced dead at the scene.
Gardaí were alerted and another man, who was also an inpatient, was then arrested nearby.
Members of the Armed Support Unit assisted in the arrest.
The ward has been sealed pending a forensic examination.
A key aspect of the investigation will be to establish a motive for the attack.
A post mortem on the dead man’s remains is due to take place later.
A Garda spokesperson said: "Gardaí were alerted to an incident involving two male patients in the hospital shortly after 5:30am this morning.
"A man in his 30s was arrested at the scene by investigating Gardaí and taken to Bridewell Garda Station, Cork where he is currently detained under Section 4 of the Criminal Justice Act, 1984."
They added that they are not currently seeking anyone else in relation to the incident.
It is understood that family liaison officer has been appointed and the family of the deceased has been notified.
Management and staff at MUH said they were "saddened and shocked at the tragic and unexpected death of an elderly patient in an incident at the hospital."
A hospital spokesperson expressed their deepest condolences to the man's family, relatives and friends.
The spokesperson added that counselling services were being provided to patients and staff affected by the incident.
A spokesperson for the INMO said they were not commenting on the incident, but the organisation had been in contact with the hospital and will provide support to any members affected by the situation.