Baby-faced Jon will play Marius - one of the main parts - at a London theatre from 28 July.
Les Miserable is very famous and is about war, love, and death.
It has been translated into 21 different languages and has been performed across the world.
Jon's character, Marius, is a romantic student who has fallen in love with a girl called Cosette.
Enders' lad
And he is no stranger to the stage.
When he was just 12, Jon played Oliver Twist in Oliver! at a big London theatre.
Before that, he was in another TV drama. But he also played schoolboy Josh in EastEnders!
The rest of the S Clubbers are making plans for their future too.
Rachel is working on solo stuff and Jo is probably going to do the same.
While Bradley wants to be a record producer and Hannah hopes to make it as an actress.
Tina hasn't told anyone what her plans are yet.
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Singing solo on stage was great!
