Alfie (Shane Richie) has been in the dark over Kat's infidelity since she started sleeping with her mystery man in July, but her deception finally comes to an end in a few days' time.
In the days leading up to the storyline's big turning point, Kat (Jessie Wallace) plays with fire even more so than usual by taking bigger risks with her secret relationship.
Although the Queen Vic has re-opened following a successful fumigation, one episode sees Kat spend an entire night away from the pub - preferring to stay with her admirer at the secret bedsit.
Kat also has a bouquet of flowers from her lover delivered at the pub, as the remaining suspects Derek, Jack, Max and Michael all watch on with big smiles.
Alfie is initially fooled when Kat makes excuses for both incidents. However, when a guilty Kat decides to focus on her marriage and begins to overcompensate with Alfie, alarm bells ring for him and he finally realises that something is amiss.
Unable to keep quiet over his suspicions, Alfie gently confronts Kat - asking whether she has told him the real story behind her mysterious night away and the recent delivery of flowers.
At first, Kat continues to lie to her husband, but he isn't satisfied by her excuses and persists by making his suspicions clear.
Realising that she cannot maintain her lies, Kat finally tells Alfie the devastating truth - there is someone else…
Continuing her honesty, Kat also confesses that she is confused about her feelings as she thinks she may have fallen in love with the other man.
A disgusted Alfie demands to know who Kat is having the affair with, but she falsely claims that he doesn't know the guy involved.
Refusing to believe his cheating wife, Alfie continues to demand answers. As his temper gets the better of him, Alfie aggressively grabs hold of Kat and pushes her against the wall.
With the Moons on the rocks, it's clear that they both have some life-changing decisions to make about their future as a couple. Is there any hope left at all for their marriage?
EastEnders airs Alfie's discovery on Thursday, September 13 at 7.30pm and Friday, September 14 at 8pm on BBC One.