Gardaí are investigating the sudden death of John Hutch who died in hospital today.
The 66-year-old was found at the bottom of the stairs at his home in Drumalee off the North Circular Road in Dublin at around 4pm yesterday.
He was taken to the Mater Hospital but never regained consciousness.
Gardaí are treating the case as a tragic incident and a file is being prepared for the Coroner's Court.
A post-mortem is to be carried out to establish the cause of death.
John Hutch is the brother of Gerard Hutch, the man known as "The Monk" who is currently in hiding because of the ongoing Hutch-Kinahan feud.
John Hutch and his son Jonathon were also targeted but survived attacks by gunmen linked to the Kinahan organised crime gang.
Another brother Edward became the fifth victim of the ongoing feud after was shot dead at his home in Dublin three years ago.