Viewers have recently seen the actor's alter ego Calvin Valentine giving into temptation after growing close to his wife's sister Mercedes Fisher, played by Jennifer Metcalfe. Their attraction will intensify over the coming weeks.
Discussing the plot, Whittle told PA: "When the storyline first came out I wasn't quite sure about it myself. Calvin's always been a very moral person and to have an affair with his wife's sister is a bit out of character."
However, the 28-year-old confirmed that he changed his mind after realising that Calvin had "gone through quite a change", making his betrayal of partner Carmel (Gemma Merna) more credible.
He said: "[Calvin] did walk away from Warren and left him to die and was in a very dark place so he does have dark side to him, this naughty side, which I think they're exploiting with young Mercedes. So it's going to be exciting."
Whittle is currently competing in the seventh series of Strictly Come Dancing and recently secured a place in the semi-final.