The BBC1 soap's executive producer Dominic Treadwell-Collins announced earlier this year that he was creating a transgender character and expressed a determination to have a transponder actor in the role. A number of transgender actors submitted themselves for the role and, working alongside groups within the transgender community, EastEnders began workshops to find an actor.
Millington's debut scenes will air later this month, but little will be revealed until Riley's permanent return at the end of 2015.
"I am extremely excited to be joining EastEnders," the 21-year-old actor said. "I can honestly say that I have now fulfilled my two biggest dreams – to be living my life as a man and to be an actor. I cannot wait to really get stuck in with filming and I look forward to seeing what is in store for my character."
Treadwell-Collins added: "From Mark Fowler’s HIV to Colin and Barry’s first gay kiss, EastEnders has always led the way in changing audience’s perceptions about ‘difference’ – and ultimately making the world a better place. It has been my intention for a long time to cast a trans actor playing a trans role – and we have been so careful to ensure that we cast the right actor for the part."
Treadwell-Collins was touched by the stories he heard in the casting process.
"I’ve sat in many acting workshops over the years with our casting executive Julia Crampsie and her team – but never have we been so moved by the incredible life stories and wealth of talent that we experienced over our several weeks of workshops with transgender actors. The people we met showed us a strength and bravery that took our breath away – and to go through as much as they have while maintaining humor and a positive view on the world is testament to what special people we met."
The show boss also insisted that Millington's casting should in no way be seen as a box-ticking exercise.
"In Riley, we have found not just a talented actor but also an inspirational young man whose warmth immediately comes through the screen. And this isn’t about tokenism. Alex Lamb and his story team have worked with Riley to create an EastEnders character who is fresh and relatable – but also comes with his own stock of secrets and is going to be thrown right into one of our biggest stories for the end of the year. I hope that the audience will take Riley and his character to their hearts as quickly as everyone here at EastEnders has done."