The actress, who plays Cora Cross, singled out the newcomer when asked to name her favourite character during a live Daybreak interview this morning (November 15).
Mitchell told show hosts Lorraine Kelly and Aled Jones: "Oh God, I like all of them. Well, I'm particularly interested in my young grandson [who's] coming in. But I mustn't talk about that!"
Pictured: Ann Mitchell on Daybreak.
Last week, EastEnders bosses announced that actor Khali Best had been cast as Dexter, who is the 20-year-old son of Cora's long-lost daughter Ava (Clare Perkins).
Speaking this morning, Mitchell said that she is delighted to be exploring Cora's past with the ongoing Ava storyline.
She commented: "It's fascinating, because you get a chance to bring a different facet to each scene.
"One of the scenes we did at the end of the day, and we did it in five minutes - we were up against the clock. That was the most emotional scene. It was strange, to do it so quickly!"
Mitchell added that the public's response to Cora has been "fantastic" and "very, very positive" since her debut last year.
She explained: "They seem to welcome the complexity. They like the darker side, and they like the funny side."
EastEnders continues tonight (November 15) at 7.30pm on BBC One.