One of Walford’s biggest secrets is out – as Grant Mitchell has finally discovered Mark Fowler Junior is his son.

EastEnders viewers have known about Mark (Ned Porteous) and his true identity for 21 years, but Grant (Ross Kemp) was in the dark – until his brother Phil (Steve McFadden) decided to reveal the truth.

Grant Mitchell’s love child Mark (BBC)

The brothers, who have often been at loggerheads, came together after Phil collapsed and was taken to hospital.

While he was unwell, Grant went off to save Phil’s son Ben (Harry Reid) from kidnappers, with Mark insisting on accompanying him.

Phil felt he needed to repay his brother – by telling him the secret.

Phil Mitchell collapsed (BBC)

“There’s something you need to know. Call this me doing something for you,” he said.

When Phil mentioned Mark, Grant gave his assessment: “He seems like a decent enough kid, which is a miracle considering who his mother is, but there you go.”

Mark is the son of Grant’s sworn enemy Michelle Fowler (Susan Tully), and the product of an unexpected one night stand in 1995.

Father and son (BBC)

His father never knew about the secret love child.

Phil explained: “I only found out a bit ago myself. Found out – Michelle, she wrote to mum just before she died. He’s – he’s your kid, Grant. Mark. Mark is your son.”

Will Grant tell Mark that he's his father? #EastEnders

— BBC EastEnders (@bbceastenders) September 6, 2016

Mark himself still does not know the truth, which Phil only discovered when he stumbled across a letter from Michelle which was intended to reach Peggy Mitchell (Barbara Windsor) before she died.

Viewers’ reactions? “Finally!!!!”

It might've taken 20 odd years but I always knew one day Grant Mitchell would find out he had a son #EastEnders

— Sarah Thurlow (@sjthurlow) September 6, 2016

I'm glad Grant finally knows Mark is his son #EastEnders

— Lori ♛ (@lori4evaa) September 6, 2016


— tobi (@Tobi_TV_) September 6, 2016