Gangster Derek Branning has been unmasked as the Walford mystery man who has been having an affair with Kat Moon, leaving husband Alfie heartbroken.
EastEnders viewers have been gripped by the infidelity, with several names in the frame in the storyline which has been running since the summer.
But in a dramatic confrontation in the BBC1 soap, Alfie (Shane Richie) discovered the truth about her fling.
He has long suspected Kat (Jessie Wallace) has been doing the dirty on him, and decided to follow her to catch her in the act.
Alfie followed her to a secret bedsit and kicked down the door, to find a room filled with candles and a bed strewn with rose petals.
After demanding to know the identity of her lover, he caught a glimpse of papers she was trying to destroy, addressed to "Mr Branning", which gave the game away.
Storming over to the Queen Vic, he rounded on Jack and Max Branning before Kat rushed over to reveal with a point of her finger that she has been seeing Derek (Jamie Foreman).
The whodunnit-style story has been rumbling on since August and is building towards a Christmas Day climax which will see Derek meeting his end.