Unlucky Leo, who is already struggling to come to terms with the brutal murder of his former wife Lana will be left reeling when Sandie announces that Shannon is his daughter and demands a paternity test.
And the Herald can reveal the paternity test will prove that Leo is in fact the father of the young girl -- leaving him with no choice but to face up to his responsibilities.
To add to his woes, Leo will also have to contend with Sandie's efforts to win him back as she pulls out all the stops to lure him back into her love-trap.
According to a spokesperson for the soap: "Thursday night's episode will see Sandie go in for the kill and make her move on Leo, but she is left rather embarrassed when he turns her down and pushes her away from him.
"Sandie was originally just meant to come over from England for a week and, while she does eventually return to England, I can say she definitely stirs up quite a lot of mischief and trouble during her stay and we'll probably be seeing a lot more of her now that Shannon is involved," they added.
Sandie, played by award-winning actress Charlotte Bradley, originally ran out on Leo after sleeping with his son Dean when it was revealed that Leo was having an affair.
Dean, who has already been tested and is definitely not the father, will also play a central role in the controversial storyline and is sure to stir up some strife for his estranged Dad, Leo.
And according to Charlotte, she couldn't be happier to reprise her role as Sandie Dowling.
She said: "I still get called Sandie. Fair City has such a big audience and people have always associated me with the character.
"People were really interested in talking to me about why Sandie left and the terrible thing she did.
"I would talk back about the situation she was in and how she was very drunk when it happened.
"I loved playing her and it was actually very hard to leave. It's great to be back," she added.
Since leaving the soap, Charlotte has starred in a string of hit movies and TV shows and is very much in demand at home and overseas.
In 2000, Charlotte took to the big screen alongside Tinseltown favourite's Kate Hudson and Stuart Townsend in the hit romantic comedy About Adam.
She has also starred in Irish blockbuster Veronica Guerin as well as made appearances in Father Ted, The Clinic, Proof, Speed-dating and Seacht to name but a few.