The actor, who was axed as Mickey Miller in 2008 after five years on the show, will return next week to film two episodes involving on-screen brother Darren's wedding to Jodie Gold.
"Typically, Mickey arrives back for Darren's wedding but he's more interested in giving his little brother a proper knees-up to celebrate his last night as a bachelor," a source told the Daily Star Sunday.
"He's pleased to see some of his old mates but when he finds out what they've planned for Darren's stag do he realises he has to take control as it's pretty dire.
"Luckily for Darren, big brother Mickey makes sure he gets one hell of a send-off before his big day."
Earlier this year, it was announced that actor Charlie G. Hawkins, who plays Darren, would be leaving EastEnders.
Swash recently signed up to star in new ITV2 game show Minute to Win It with Caroline Flack.