A star-studded cover version of the 1960s Beach Boys hit God Only Knows, apparently.
The single, which aired with a blockbuster video for the first time last night, marks the launch of BBC Music and will be sold to raise money for the Children in Need appeal.
Sir Elton John, wearing a suit made of butterflies, no less (#ELLEWedding) was the only member of the line up to have appeared in the BBC's first collaborative charity single of the kind, the 1997 cover of Lou Reed's Perfect Day.
The video is so jam-packed full of big names that you could blink and miss one – but we've spotted Kylie trapped in a bubble, Chris Martin reclining on a piano, Chrissie Hynde sitting on the moon, Florence Welch wearing jungle-camo, a be-winged Lorde, the song's original writer Brian Wilson, and a tiger. Oh, and Dave Grohl (no idea what he's doing there, but we're not complaining).
Can you spot all 27 of them?