Rhona has started to get on with her life after her traumatic time with Pierce, who is now in jail for raping her, and is stunned when Marcus arrives in the village.
Marcus's intentions are initially unclear and Rhona is forced to decide whether to take the handsome youngster at face value and forge a relationship with him, potentially re-opening old wounds in the process.
"When my agent sent me the character of Marcus Dean, I was quietly smiling inside," said 30-year-old Grey. "We share so many similarities, both the good - and perhaps - some of the bad! I thought 'I know who this kid is'.
"To then get the call to say that the role was mine was one of those pinch-yourself moments we actors simply dream of.
"For Marcus, the battle of being torn between wanting to forget his relationship with his Dad but also ultimately, wanting to simply be loved is a challenge many of us face, and one that I hope I can bring some truth to.
"He is such an open book, with such an uncertain future that I just can't wait for you all to see where his journey in the village takes him!"
Emmerdale producer Kate Brooks added: "Marcus' arrival will certainly ruffle a few feathers and flutter a few hearts in the village. However, people will soon realise there's more to Marcus than merely being the son of Pierce.
"But will our villagers give him a chance, or will he be forever doomed to live in the shadow of his father's heinous crimes?
"We're delighted to welcome Darcy to the show and we're sure he'll certainly make quite the impression on villagers and viewers alike."
Marcus will first appear in the episode being broadcast on Thursday, February 3.