Craig Moon, who has Down's Syndrome, will make his first appearance on screen in the autumn when family patriarch Eddie Moon arranges for Michael to meet the sibling he never knew existed, according to The People.
Elliot Rosen, 32, has taken on the role of Craig and is thought to have already filmed his first scenes. Reports suggest that he has been signed as a guest artist for a handful of episodes.
EastEnders bosses are believed to have worked closely with the Down's Syndrome Association while devising the new storyline for the Moon clan.
A Walford source told the newspaper: "It is something they are very proud of. They are determined to continue to raise issues like this."
Meanwhile, praising the soap's decision, a spokesperson for the Down's Syndrome Association commented: "Presenting people with Down's Syndrome living successful lives is always positive."
Michael, played by Steve John Shepherd, was the first of the new Moons to arrive on Albert Square - making his debut last year.
David Essex, Tony Discipline and Matt Lapinskas were later unveiled as other additions to the family, landing the roles of Eddie, Tyler and Anthony respectively.
Read more about the Moons and their current EastEnders storylines:-
> EastEnders arson attack 'devastates Eddie Moon'
> EastEnders newcomer Anthony 'was corrupted by Michael'
> EastEnders star promises "shocking" Eddie scene
> Matt Lapinskas: 'I was nervous over EastEnders debut'
> EastEnders' Matt Lapinskas: 'Anthony receives a big shock'
> EastEnders' Steve John Shepherd: 'Michael is capable of killing'
> Digital Spy's full EastEnders spoilers
Watch EastEnders' Anthony and Tyler Moon teaser video below: