The soap's baby swap storyline finally reaches its climax this Friday as Ronnie comes to her senses, tells Jack that Tommy is not his son and heads over to the Queen Vic with the intention of putting things right.
Next week, after she has come clean, fans will see Ronnie spend time in jail as her crime is investigated. Meanwhile, Jack is left reeling following the news that his baby son James was the child who died on New Year's Eve.
Pictured: Jack is devastated as the truth sinks in.
In an interview with Inside Soap about Jack's role in the aftermath of the baby swap reveal, Maslen explained: "He couldn't believe what Ronnie was saying when she tried to tell him about James, but now he's heartbroken.
"At first, he just couldn't understand what she was on about and thought she was saying it to be spiteful. He doesn't believe it until he hears the results of [a] paternity test, and then he's completely lost."
Discussing how Jack has to say goodbye to Tommy as Kat and Alfie get him back, the actor continued: "Jack is distraught - he loves the baby like he's his own. It feels like losing his own child. Jack can normally cope when things go wrong, but this situation has brought him to his knees."
Maslen also pondered what the future could hold for Jack and Ronnie, who tied the knot late last year.
He said: "Jack loves Ronnie. There's an unbreakable bond between them. One day, he might even be able to understand why Ronnie did what she did."
> Read our full spoilers for next week's EastEnders episodes