One Direction landed the opening, an honour that previously went to Chris Martin, Kylie and originally Paul Young.
Band Aid organiser Bob Geldof had said that section was the "hardest" to sing because being the first, it's the most recognisable.
He was impressed with how "sad" the 1D lads made the opening, almost "whispering in" the first few words.
Some of the Band Aid 30 artists including Ed Sheeran, Ellie Goulding and Emeli Sande recorded solo versions of the entire track, allowing producers Paul Epworth and Midge Ure to then cherry pick who sang which line best.
Bob Geldof mentioned how each full performance he'd witnessed was great on its own, making him want to release multiple takes of the song.
It's an option for the CD single, which is expected at the beginning of December, although the current plan for that is to include the three previous Band Aid recordings (from 1984, 1989 and 2004) alongside some remixes of the new version.
Clean Bandit had the task of scoring some new string parts for the track. That meant Neil and Grace from the band got to play violin and cello on the song, but they also sing on the big chorus at the end as well.
Grace Chatto admitted she was smiling and dancing for that but as a group, all the acts had been told off for looking too serious as they sang the famous "feed the world" phrases (which now includes "feel the world" and "heal the world") so they all had to re-do it.
As if it was ever in doubt, Bono gets to do 'his' line again (even though the lyrics have changed from "well tonight thank god it's them instead of you" to "well tonight we're reaching out and touching you").
Bob Geldof did say he'd asked Chris Martin if he wanted to have a go at that line. Chris didn't want to.
Sinead O'Connor stayed over at Bob Geldof's house the night before the recording and had specifically requested the phrases she wanted to sing as they meant the most to her ("why is comfort to be feared, why is touch to be scared").
Jessie Ware appears in the group chorus but doesn't get a solo line to sing in the version that was shown on The X Factor on Sunday night.
Rita Ora was only at the recording for 90 minutes on Saturday, as she had to race in and out to complete filming commitments on The Voice.
Most of the other acts arrived first thing in the morning and hung out for the best part of the day. The end chorus which required everyone to be together, was due to be recorded mid-morning, but got pushed back as Bono was late.
He said he was "embarrassed" to keep everyone waiting but his plane had been delayed due to fog.