This concert is the band's swan song.
swan song
idiomA final performance or accomplishment, especially one before retirement.
Origin
disputed originCalque of German Schwanenlied(from Schwan + Lied) or Schwanengesang; from the belief that the mute swan sings before dying.
The veteran athlete announced that this championship game will be his swan song before he retires.
The aging novelist spent years crafting her final manuscript, intending it to be a brilliant swan song to her long and celebrated career.