But the big question is whether the U2 frontman will be there this year after his appearance last year sparked security concerns when thrilled fans flocked to see him in action.
He had joined a team of Irish musicians that included Mundy, Declan O'Rourke and Hothouse Flowers rocker Liam O Maonlai to busk for homeless charities.
He did the same thing in Christmas 2010 and 2009.
However, gardai had to remove the stars from Grafton Street to St Stephen's Green park because of safety concerns sparked by over-enthusiastic fans.
Now an inside source says there's no guarantee he'll even be back this year as it's always an "impromptu thing" for the Dublin star.
She said there was no way of telling in advance if he'll be making an appearance or whether extra security would have to be drafted in for the busking session.
"He was in town last year shopping and he just decided to join in the sing-song again. It was purely a spontaneous thing."