Brian Slater has never appeared on screen but has been mentioned numerous times.
Brian is the husband of Jean Slater and father of Stacey Slater and Sean Slater. Brian died in December 1999 after a fight with his son Sean punching him. This caused him to suffer a brain hemorrhage and die while working on a building job.
The key given to Stacey by Sean was for a safety deposit box and Brian left for all of them.
Kyle's mother had the same key to the safety deposit box. She cleared it out when she found out he'd died. It contained photos, birth certificates, letters and marriage certificates. Kyle’s mother and siblings didn't know about Jean, Stacey and Sean either, until Brian died. Even then, Kyle's mother wouldn't tell anyone.
On Kyle's 21st, his mother wrapped the stuff from the safety deposit box and sent it to Kyle as a present. As she wanted to hurt him as they don't get on, Brian left a letter in the safety deposit box for Kyle, Siobhan, Shannon, Sean and Stacey.
Kyle doesn't really remember his father. He was only five when he died. He’d remember building sandcastles in Norfolkand and sticking little flags in them. He’d fill a bucket with water and make moats around them.
He has never appeared on screen but seen in a photo in an episode (seen 07/07/2015).