The character was last seen in Albert Square over two decades ago - but long-term viewers have now got an update about the former Walford resident.
EastEnders has shared a heartbreaking update on an absent character - more than two decades after they bowed out.
Lynne Slater - played by Elaine Lordan - was last physically seen on the BBC soap in 2004, having debuted in 2000.
The older sister to Kat (Jessie Wallace), she left Albert Square behind after giving birth to a stillborn daughter.
In Monday's (March 16) episode, Kat - who is currently staying with Lynne - FaceTimed her family in Walford for Mother's Day.
She informed daughter Zoe (Michelle Ryan) and son Bert (Elliot Briffett) that Lynne's dog was dying.
It came as Bert asked: 'Has auntie Lynne’s dog died yet?'
Kat Slater gave her family a sad update during a Mother's Day FaceTime call - and it concerns a character not seen in Walford for decades
Lynne Slater, Kat's older sister, featured on the BBC soap from 2000 until leaving in 2004 (pictured in 2003 with then-husband Garry Hobbs)
Kat told the pair: 'Not yet darling, but it’s on it’s last legs and Lynne won’t stop crying.'
Lynne arrived as one of the original Slaters, alongside dad Charlie (Derek Martin) as well as sisters Kat and Little Mo (Kacey Ainsworth).
They were also joined by grandmother Big Mo (Laila Morse), Lynne's now ex-husband Garry Hobbs (Ricky Groves), as well as Zoe - who was publicly believed to be Charlie's youngest daughter at the time.
The character returned off-screen in 2016 for Charlie's funeral, but as implied, audiences didn't get to see her.
It comes amid a soon-to-be turbulent time for the Slaters, as Zoe is set to be reunited with her long-lost son, Josh (Joshua Vaughan).
He is joined by adoptive mother Sandra, who is portrayed by Holby City alum Dawn Steele.
Speaking to The Sun ahead of Sandra's debut, the actress said: 'I was thrilled to be asked to play the role of Sandra who arrives and throws a spanner or two into the Square!
'It was so great to go back to Elstree after the end of Holby City. Lots of the same crew (and a few cast!) are still there so it was joyful to see them all again.'
The actress added that she was warmly welcomed back to the studios and enjoyed adapting to the soap's different filming style.
But she revealed it was ultimately Sandra's dramatic storyline that convinced her to sign on.
She continued: 'But it was Sandra’s storyline and character that really made me want to do it and I’m sure viewers will be thrilled with another piece of the puzzle ahead of the trial, Sandra’s timing couldn’t be better, or worse.'
Viewers have already seen Zoe reunited with one of her twins, Josh's sister Jasmine Fisher (Indeyarna Donaldson-Holness).
The pair both lived on Albert Square for months, although Zoe was in the dark at first about Jasmine's true identity.
Not long before his demise, Anthony Trueman (Nicholas Bailey) learned he fathered the twins with Zoe Slater (Michelle Ryan) in 2006.
They later had a confrontation resulting in Anthony's death - and while Zoe was charged with murder, the BBC soap confirmed she is not the culprit.
Lynne and Kat arrived with the rest of the original Slaters - dad Charlie (Derek Martin), sister Little Mo (Kacey Ainsworth) and Zoe (Michelle Ryan), Kat's daughter and supposed 'sister' at the time
On January 15 viewers found out Jasmine murdered murdered her biological father in the Queen Vic pub.
This revelation came as Jasmine visited Anthony's body in the chapel of rest, along with grandfather Patrick (Rudolph Walker) and extended family.
Stood over her father's coffin, she played a video of him attacking Zoe, with an off-camera scuffle between the unknowing father and daughter ending in Anthony falling, motionless.
Addressing his corpse, Jasmine said: 'You could have killed her. But I stopped you.
'It’s nice to finally meet you, dad. Now rot in hell.'
Reacting to the reveal, one fan wrote on X: 'Jasmine killed her dad [Anthony]. Jean was right about Jasmine she is the murder suspect, she did it.'
Another said: 'So Jean was right, how long before everyone else does.'
A third remarked: 'I knew she did it. However it seems it was accidental and self-defence, not planned.'
A fourth chimed in: 'I wouldn’t have made Jasmine the killer TBH.'
A fifth commented: 'Jasmine getting arrested killed Anthony.'
While a sixth pointed out: 'So that tiny girl, while recording on her phone with one hand, took down a 6 foot bloke with some random object in the other. What!?'
EastEnders airs on BBC One and is available to stream on iPlayer.