Sean, who Keith hailed as a "courageous and brave warrior", died peacefully surrounded by his beloved family at Connolly Hospital in Blanchardstown on Saturday.
A service for the Dubliner, who lived in Celbridge but was originally from Raheny, will take place on Thursday at Glasnevin Crematorium.
Earlier, Keith and his son Jay said on social media: "Words cannot describe how heartbroken we are to announce the passing of our father/grandfather Sean.
"The most courageous and brave warrior we've ever known and probably will ever know. We already miss him so much."
A notice on RIP.ie reads: "The death has occurred of Sean Duffy (peacefully), surrounded by his loving wife and three sons, at Connolly Hospital Blanchardstown, Sean, beloved husband of Patricia (Pat) and dear father of Derek, Keith and John.
"Sadly missed by his loving wife, sons, sisters Carmel and Margaret, daughters-in-law Rose and Lisa, brothers-in-law, grandchildren Jordan, Mia, Ailbhe, Tadhg, Lily and Dylan, nieces, relatives, neighbours and friends.
"Removal on Thursday to Glasnevin Crematorium arriving for Service at 2pm. House Private Please."
In the condolences section, one person has written: “I'm so sorry for your loss my condolences to you and your family Relations and friends my thoughts and Prayers are with you all may your Father R.I.P.
"Thinking of you all at this sad and difficult time.”
Another has added: “I am so sorry Pat on loss of your lovely husband Sean great memories of our time in Grangemore. My deepest sympathy to you and the boys xxxx.”
One person left a message, saying: “To Pat, Derek, Keith, John and family. So sorry to hear that Sean has passed away. Great memories of Sean over the years especially as he sang at my wedding also. Great friends to my own late mam and dad. Sending u all my sincere sympathy at this very sad time. all our love."
While another said: “Condolences and sympathy to the Duffy family. Fond memories of a gentle soul and lovely man.
"Very customer-focused and a pleasure to shop in Frawleys in Dublin's inner city when Sean worked there. Rest in peace dear man and may the lord bring comfort to all your family at this time.”