Charlton were relegated from the English Premier League after losing 2-0 at home to Tottenham Hotspur on Monday.
They follow already-relegated Watford through the trap door to the second division, leaving West Ham United, Wigan Athletic and Sheffield United to scrap it out to avoid joining them.
Tottenham's win lifted them into sixth place and into a UEFA Cup place, which they have a good chance of securing since they have a game in hand on the other contenders for Europe.
Charlton got off to the worst possible start, allowing Tottenham's Bulgarian forward Dimitar Berbatov space to run and shoot into the right-hand side of the goal in the seventh minute for his 11th league goal of the season.
Striker Jermain Defoe, a former Charlton player, sealed his old club's fate with a fine effort a minute into injury time.
Charlton remain on 33 points with one game left. In the three-way fight to avoid the other relegation place, Wigan are on 35 with a game remaining. West Ham and Sheffield United both have 38, also with one game to play.
