Could this be the biggest EastEnders curveball of the last decade?
Well, Shane Richie certainly thinks so.
Speaking with the Radio Times, he said: "It's the biggest curveball I think Alfie has ever been thrown in the 13 years that I've been here. I've told very few people about it.
"It will be interesting to see the reaction. Just when you think they're [Alfie and Kat] finding happiness, something like this happens."
The soapstar continued: "It's a dark secret that Alfie takes to Ireland with him. The audience will know, but no one else will."
And, in true Alfie style, it seems as if he'd rather pretend that nothing is wrong and go on a runner, rather than own up to things.
"He just wants to go," continues the actor.
"It's typical of Alfie to put his head in the sand and not acknowledge what's just happened. And that really is evident in the very last scene. You just kind of think, 'Oh, Alfie!'"
A six-part EastEnders spin-off show starring Alfie and Jessie Wallace, who plays Kat, is due to air in 2016.
Their characters will bid goodbye to Albert Square - for the time being - next week.
Speaking about their new series, Shane said: “We'll find out who Kat and Alfie really are and the dark secrets they've kept for years and where they're going. It's going to be mystical, dark, explosive, and it's also going to be beautiful."
What do YOU think Alfie’s dark secret could be? Let us know via the comments box below now.