Macaulay Gillephey curled the sweetest free kicks at home to shoot Charlton back to the championship.
It has been five long years for the addicks in League One, but the defender came Trumps with a 30th minute effort to earn Nathan Jones promotion in his first full season as a boss.
Charlton has been out of the Premier League since 2007 and this is their fifth season in League One and the eighth of the last nine.
But since Nathan Jones took the lead in February 2004, things are in the valley – free from an unimaginable relegation struggle for a third place this season.
The game started at a great pace.
And Ref Andrew Kitchen decided to keep the card in his pocket when Lloyd Jones was dazzed while the Orient Striker seemed to break into half of Charlton.
Right-back Ethan Galbraith, who, according to Wellens, said that a “future Premier League football player” has dragged an attempt wide.
Ollie O'Neill had the chance to shoot when the O's Charlton caught during the break, but Kayne Ramsay threw himself to block the effort.
Leyton Orient came close to breaking the impasse when Agyi played a peach of a cross from the right, but Jordan Brown was unable to connect.
And Charlton punished them relentlessly on the other side when Tyrese Campbell was brought 25 meters from the goal.
Up stepped Macaulay Gillephey to curl a beautiful free kick past Josh Keeley, even though the keeper led his fingertips for his sixth goal of the season.
It was so well executed and sent the sold-out Charlton end in a row of jubilation
What had been so frustrating for Orient is that in the first half their best -scoring Charlie Kelman did not get a single kick in the Charlton Box.
Wellens sent his team to the second half early and Galbraith managed to get to the right flank behind the addicks, but his cross was jumped by Will Mannion.
And Orient went enormously close to leveling when Jack Currie saw his effort deflected by Tyreece Campbell barely a centimeter wide of the right pole that the Mannion had beaten.
The fans of the O, who had become a bit silent, now found their voice again, because they believed that they might be able to claw back in the game.
The bar then came to the rescue when Currie drove forward, played a pass in Kelman, who let an attempt of 20 meters fly over Mannion but rattled back from the woodwork.
Alex Gilbert took Jamie Donley on the edge of the box before the player cut off himself, but shot his shot against the wall.
Conor Coventry saw an effort tipped by Josh Keeley after he was played by Karoy Anderson.
Ref Andrew Kitchen had problems with his communication kit and there was a long delay while he was caught by a replacement.
Chuks Aneke saw a snap shot pushed around the pole.
After 11 minutes of stopping it was finally over and the addicks are back in the championship.