Earlier today, show bosses confirmed that the identity of Kat's secret lover will finally be revealed on Thursday, December 20, when Alfie takes action to find out whether he can really trust his wife.
Viewers will see Alfie tell Kat (Jessie Wallace) that he needs to go away for the night, but his real intention is to secretly stick around in Walford and keep an eye on what she gets up to.
When Alfie follows Kat to a bedsit on Bridge Street, he is determined to discover the truth once and for all, so he smashes the door down to find her.
As the Moons have another showdown over their troubled marriage, Alfie is shocked to discover that Kat's secret lover is one of the three Branning brothers.
Richie told Inside Soap: "This really tips him over the edge, and Alfie becomes a monster. He finally gets some balls and decides enough is enough. He tells Kat that he doesn't care about her anymore - he says she's filthy and disgusting."
He continued: "Alfie has kept going with Kat for the sake of their love and their history. But if he can't forgive her for this latest indiscretion, there's no way they can keep their family together.
"Jessie and I had a vested interest in getting this right, because our bosses gave us such a great opportunity. We spent a lot of time working on it - and I hope we've ticked every box."
Richie added that he was kept guessing over the identity of Kat's man for quite some time.
He explained: "When we were first told Kat would have a secret lover, I really thought it was Michael. Mind you, I really thought it was Ray at one point! So when we were finally told who it was, I went, 'Ah, I get it!' It's all very clever."
EastEnders continues tonight (December 3) at 8pm on BBC One.