EastEnders has delivered another bombshell storyline twist, revealing that Kat Moon has a secret son she knows nothing about.
Kat gave birth to twins in 1984 when she was only 14 years old, but she only remembers the arrival of one of the children - her daughter Zoe Slater.
The truth was revealed to viewers in Friday evening's emotional episode (May 1), which saw Kat pay a visit to the convent where she remembered giving birth to Zoe.
Kat confided in a nun called Sister Ruth (June Whitfield) who had been at her side at the time, but once Kat left it became apparent that Sister Ruth knew one vital detail that she didn't.
Checking the 1984 birth records to verify her suspicions, Sister Ruth found an official note from Kat's previous visit which read: "February 1, 1984. Kathleen Slater, 14. Live births - 2. One girl and one boy."
Sister Ruth makes a discovery
© BBC
Sister Ruth makes a discovery
As Sister Ruth only did her digging once the visit was over, Kat remains completely unaware of the life-changing revelation.
Show bosses are keeping tight-lipped about all further details, leaving fans to wonder whether the secret of Kat's son could take centre stage in EastEnders' upcoming Ireland-based spinoff featuring her and husband Alfie.
Some fans are also speculating that Stacey Slater's brother Sean is the mystery man in question - could it be that Jean isn't his biological mother after all?