The soap actor best known for playing Kat Slater in the BBC One series is mum to daughter Tallulah, 17, and proudly shared a snap of the newborn baby on Tuesday along with his name.
In a black and white photo, the baby is seen sleeping with Wallace captioning it: "Welcome to the world , my grandson SJ. You are loved, cherished and adored."
Wallace shares daughter Tallulah with her policeman ex, Dave Morgan, although they split shortly after her birth.
Some of Wallace's famous pals congratulated her on the new addition to her family, with EastEnders star Lacey Turner commenting "Beautiful boy" while the soap's Suki Panesar actor Balvinder Sopal and Blue popstar Antony Costa both offered their congratulations, although the Instagram post announcing her grandson's arrival has since been removed.
Wallace is not the only soap actor to have become a young grandparent - former Coronation Street star Kym Marsh, 45, is about to become a grandma for the second time after welcoming her first grandchild in 2019, and EastEnders actor Danny Dyer became a granddad at 43 when his reality TV star daughter Dani had her first child.
Soap star Wallace has played Kat Slater on and off since 2000, leaving and returning to the role a number of times.
She has also featured in 2017 spin-off series Kat & Alfie: Redwater with former EastEnders co-star Shane Richie, who played her character's husband Alfie Moon.
It saw the then-couple move to a small Irish town which was hiding some dark secrets and eventually led to Kat's return to Albert Square.
EastEnders has recently undergone a schedule shake-up along with ITV soaps Coronation Street and Emmerdale, and this week unveiled a refreshed set for the show.
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