It's the storyline that has been dragged out since the summer, leaving some viewers wondering if they would ever find out Kat Moons' secret.
But tonight the truth finally came out as it was revealed that the EastEnders' landlady has been having an affair with Derek Branning.
And in true soap style, no revelation would be complete without a screaming match and someone being thrown into the street.
Viewers watched as her long-suffering husband Alfie Moon, played by Shane Richie, finally discovered who Kat, played by Jessie Wallace, has been sleeping with before throwing her out of the pub they run together.
During the half an hour episode, Alfie followed Kat to the bedsit where she has been seen on a few occasions waiting for her lover since the storyline began in July.
Demanding answers from his wife, he found out that it had to be one of the Branning brothers after he saw the tenancy agreement at the bedsit. He then confronted the brothers - Max, played by Jake Wood, Jack, played by Scott Maslen, and Derek, played by Jamie Foreman.
But Kat denied it was Max and finally admitted it was Derek after Alfie demanded that she told him the truth and she said: "It's him - it's Derek!"
Alfie then threw Kat out of the pub - and out of his life for good.
Fans of the show, no doubt relieved that the truth has finally come out, took to Twitter in their droves and gave the soap NINETEEN trending topics.
One user, Ryan Love, wrote: "So impressed with @realshanerichie's performance tonight. Poor Alfie!"
Another, called Rach, didn't seem particularly happy with Kat's choice of Branning brother and said: "Why would you have an affair with Derek? Out of everyone in EastEnders, Derek? Really?"
But Kat's revelation actually manages to bring new love into Alfie's life after he embarks on a relationship with bar maid Roxy Mitchell, played by Rita Simons, after he finds out about his wife's betrayal.
Speaking to Digital Spy, Richie said: "I think Rita Simons is now playing a different kind of Roxy, as the character is seeing somebody who she could spend the rest of her life with.
"At the same time, though, Roxy is feeling a little bit insecure because this relationship has happened very quickly. Roxy worries that Alfie might be on the rebound and could end up going back to Kat."