Fans of Steve Pemberton and Reece Shearsmith were shocked last night when characters from one of the duo's other famous shows turned up on Inside No 9.
The anthology is currently airing its fifth series on BBC Two, telling a fresh batch of stories that borrow from both the comedy and horror genres.
The latest episode, titled Death Be Not Proud, starred Jenna Coleman and Kadiff Kirwan as a young couple moving in to their first home, only to find themselves haunted by seemingly paranormal activity.
It isn't long before an eccentric bunch of characters from BBC Three's short-lived Psychoville turn up at the door, including Maureen and David Sowerbutts (Shearsmith and Pemberton respectively).
Sarah Solemani and David Bamber reprised their roles from the cancelled show, while Shearsmith's fan favourite character Mr Jelly also made a long-awaited return.
The episode has been a tightly guarded secret in the year since it was filmed, Pemberton revealed in an interview with The Telegraph.
He said: "Most shows, if they’ve got a special episode like this, they shout about it from the rooftops and we’ve done the complete opposite. Because the notion of having something unexpected or a lovely surprise like that is what Inside No 9 is all about. I don’t think it will have broken the internet, but I hope it dented it a little."
Eagle-eyed fans of the writing duo may have clocked the twist beforehand, as Death be Not Proud was laden with clues of Psychoville's impending arrival, not least the same flat and exterior setting.
Pemberton also spelt out the word "Psychoville" using the first letters of a series of tweets posted before the show aired.
Not content with a two-series crossover, the episode also contained a reference to Edward Buchan, the character that Pemberton played on ITV's drama series Whitechapel.
A number of people, including star Kadiff Kirwan, took to Twitter to give their thoughts on the episode and its big surprise.
Inside No 9 airs on Mondays at 10pm on BBC Two.