When Sharon Watts and Kathy Beale attend Gavin Sullivan funeral, they come across Zack who makes a toast to Gavin, stating how much of an awful man he was. Sharon is shocked that someone shares her hatred of Gavin, and is taken a back when Zack makes a run for it after angering Gavin's cousins. Zack sneaks into Kathy's car and watches as the cousins smash up his own car. Before leaving the funeral, Zack reveals Gavin was his dad, leaving Sharon and Kathy speechless.
He arrives on the square and moves in with his sister, Sharon, and his nephew, Albie. He starts a relationship with Nancy Carter and also has harmless flirts with her sister, Frankie. As Zack takes Frankie on a driving lesson, he stops off at the pub and has a few drinks and continues with the lesson. Zack starts to flirt with Frankie as she is driving and winds her up and as Frankie takes her eyes off the road, she hits something - it's Nancy. Despite this, he and Frankie cover up their tracks but Frankie becomes too guilt ridden and tells Mick. He decides not to tell Nancy and keep their secret. Zack is warned off by Mick not to go near his daughter but he can't stay away and Nancy asks him to enter a secret relationship with her. He agrees and they sneak around. However, Mick finds Zack's sock in the living room and once again warns Zack off. But he still doesn't listen and he goes back to Nancy. As they are fooling around upstairs, Linda is in trouble downstairs in the Vic because burglars have broken in wanting to take the charity money Whitney raised for Autism. Zack goes downstairs in his boxers and scares away the burglars. Linda and Mick are thankful and give Zack a chance but Mick tells him for a third time to not hurt his daughter again.
On 2 September 2021, Zack decides to tell Nancy that he and Frankie were the ones that hit her with the car. Nancy is heartbroken and angry and decides to break up with him.
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