The Holly and the Ivy
The words are a traditional English carol collected in Gloucestershire by Cecil Sharp and published in 1911.
The tune comes from France, and is arranged here by June Nixon, one of Australia's best known organists, choir trainers and composers. Dr Nixon has been Organist and Director of Music at St Paul's Cathedral Melbourne since 1973
The scene will be the same as it has been for decades: King's College choristers in their white and red robes, performing classic Christmas carols for a television audience of thousands.
But there is one voice that was almost missing this year. It is that of Alex Stobbs, the terminally ill musical prodigy who has defied doctors' orders by leaving hospital to sing in the service one last time.
The frail student, who moved millions with his stoicism in a Bafta-nominated Channel 4 documentary titled A Boy Called Alex, suffers from a virulent form of cystic fibrosis. His lungs, bones and digestive system are gradually being destroyed.
At the age of 20, his lung capacity has fallen to a critical 38 per cent and he is losing his hearing.
He is kept alive by a cocktail of 50 tablets by day and oxygen by night.
But the determined musician ignored medical advice to take part in Sunday's recording of Carols From King's, which will be broadcast on BBC2 on Christmas Eve.
He is in his final year studying music at Cambridge University, so it is his last opportunity to join the festive performance.
Mr Stobbs said: 'I have been in hospital for the last three weeks as my body just needed some time to recover.
'Doctors want me to be in hospital now but Christmas is the best part of the year at university and I wouldn't miss singing in the choir for anything.
'My lungs certainly aren't what they were and it's a struggle to sing, but I manage.
'This will be my last year singing in the choir and I'll be very sad to leave as it's such a wonderful institution.'
Mr Stobbs also hopes to be well enough to perform in the popular Nine Lessons and Carols Service on Christmas Eve, which is broadcast live around the world on BBC radio and attracts queues of spectators from 7am.
The chorister, from Horsmonden, Kent, originally joined the King's College choir at the age of nine.
He left at 13, when he won a music scholarship to Eton College, but auditioned again three years ago when he secured a place at Cambridge University.
In 2008, a Channel 4 documentary showed him conducting Bach's Magnificat aged only 18, and in 2009 he published a diary titled A Passion For Living.
Although his lungs are deteriorating, he wants to avoid a transplant for as long as possible because of the risks involved.
Years of steroids have also left him with brittle bones and he often uses an electric scooter to travel around campus.
Mr Stobbs, who conducts a musical group called Stobbs Scratch and hopes to become a full-time conductor, is planning to go to music college in London when he graduates from Cambridge next year.
He said: 'I'm worried about my health but I'm happy that I'm doing everything that I want to with my life.'