A Jacob Greaves own goal 15 minutes from time was enough to give Charlton a 1-0 Sky Bet League One final-day win over champions Hull at The Valley, but it ultimately was not enough to secure a late play-offs berth for the Addicks.
The home side welcomed Grant McCann's title-winners onto the pitch with a guard of honour before spending the first 10 minutes under sustained pressure from the promoted side.
Nonetheless, Nigel Adkins' men weathered the storm and grew into the game, nearly breaking the deadlock five minutes before half-time when Conor Washington brought down a ball into the box with a superb first touch before firing just wide of goal.
The two sides traded chances thereafter, and the ball pinballed off a number of players before Greaves had an unwanted final touch for the only goal of the game after 75.
While Charlton needed a win to have a chance of finishing sixth, Oxford cruised to a 4-0 win over Burton elsewhere which meant their victory over the division's best side would be their last game of the season.