Dubliner Sir Bob Geldof and One Direction's Niall Horan, from Mullingar, yesterday led many of the music world's biggest stars in London to record a new Band Aid song to raise money for the fight against the Ebola.
"BandAid30" will be released on Monday with a video shown on The X Factor TV show tonight.
The new version of "Do They Know It's Christmas?" with different lyrics was recorded on the 30th anniversary of the original song, which raised some €10m for famine relief.
UK Chancellor of the Exchequer, George Osborne, has agreed to waive VAT on the single.
He tweeted: "Just spoke to the remarkable Bob Geldof. Told him we'll waive VAT on BandAid30 so every penny goes to fight Ebola."
Fans gathered at Sarm Studios in Notting Hill, west London, where the original was also recorded, to try and catch a glimpse of One Direction, Paloma Faith, Bono, Disclosure, Jessie Ware, Ellie Goulding, Clean Bandit and Emeli Sandé as well as Chris Martin of Coldplay and a host of other performers
Bono of U2 said: "I just wish we didn't have to do this. There will come a time when we won't. And it will be great not to see the same old faces."
There are subtle lyric changes to link the new recording to the Ebola crisis.
A new line reads: "Where a kiss of love can kill you - And there's death at every tear."
Niall Horan, of One Direction, said: "Hopefully it gets to number one and raises a lot of money for a really worthy cause.
Sir Bob Geldof said: "It really doesn't matter if you don't like this song - buy it.