The entertainer - best known for being a member of Blue - announced his new role via Twitter, saying: "Thrilled 2 finally announce & confirm I am about 2 start a new chapter in my life as a full time member of the @Hollyoaks cast. Can't wait."
Among those who sent their well wishes were Robin Windsor and former X Factor contestant Rachel Adedeji, who recently joined the Channel 4 soap as well.
"Congratulations & welcome to the @Hollyoaks fam," said Rachel. "You'll have so much fun here, such an amazing, talented bunch of people. X."
Duncan's character is called Ryan. Not much is known apart from the fact Ryan is a 'good guy' who moves to the village with his family this summer.
A rep said: "Ryan is a good guy in a committed relationship. He is a grounded family man with principles and integrity but who will fight tooth and nail for what he believes in."
Duncan, 38, said: "I am absolutely thrilled to be joining the Hollyoaks team! I'm looking forward to working with the fantastic on and off screen talent on the show and bringing the character of Ryan to life."
We can't wait!