Chart stars JLS are passing their musical skills to a team of rugby legends who will try to perform in front of 82,000 fans at Twickenham.
The boyband pin-ups have been coaching stars including Austin Healey, Bill Beaumont and Brian Moore as part of their Sport Relief efforts.
The sportsmen will be singing Proud, JLS's official single for the charity, before England's final RBS 6 Nations game against Ireland.
The 23-strong group of rugby players - The Sport Relief Big Hitters - have also been receiving training from vocal coach Zoe Tyler ahead of their musical moment on the pitch.
Healey said: "There have been many times in my life when I've been filled with nerves and adrenaline before a big game, but nothing compares to the terror of singing live in front of a full house at Twickenham."
Another member of the chorus, Mike Catt, said: "We've all had some practice singing in public as we've all belted out the national anthem before kick-off, but I don't think that compares to having to sing in tune for three minutes.
"The boys and I are going to give it everything we've got. I just hope we don't hit a bum note."
The group will perform once again - accompanied by JLS - during the Sport Relief Night on BBC1 on Friday, March 23.
JLS's version of the song is released on Sunday to download and will be available on CD on Monday to raise cash for the charity.