A coach on Dublin's GAA circuit will have divided loyalties in Croke Park this Sunday.
John Mulligan from Rathfarnham is originally from Donegal and, despite training players who have gone on to play for Dublin, he says he'll have to cheer for Donegal in the semi-final clash.
The retired detective superintendent from Dun Laoghaire Garda Station says the rivalry is so fierce in his own house that his two sons removed his Donegal flag from outside the house yesterday!
John (right) has been training teams for Ballyboden St Enda's for decades.
He says: "I have worked with two of the current senior panel, Darren Nelson and Michael Darragh MacAuley. But I'm still a Donegal man.
"I support Dublin throughout the year because I've had great contact with football here for over 30 years.
"But the only time I shout against them is when Donegal are playing. Donegal played against Dublin in Cavan in the younger championship last year and I was shouting for Donegal, but I was able to congratulate Darren Nelson, who came up along the age groups with me, in the end when they won."
John says he is confident that Donegal fans will set up camp on Hill 16 next month because he says Dublin won't make it to the All-Ireland final.
"This is the first sell-out this year. There's fierce demand in Dublin but we'll let that go because we don't anticipate that they'll be in the final and there'll be plenty of space for us on the hill for the final.
"My two sons are massive Dublin supporters and they're in the same age groups as the two guys on the Dublin team. I'll be roaring for Donegal and the two guys will be on either side of me shouting for Dublin."