Ross Kemp was "taken aback" when Dame Barbara Windsor couldn't remember who he was.
The 'EastEnders' actor visited his former co-star and on-screen mother's home for his new two-part ITV series 'Living With Dementia', and he couldn't help but be shocked when Barbara - who was diagnosed with Alzheimer's disease in 2014 - forgot him during an off-camera conversation.
Writing for The Sun newspaper, he said: "'Who are you? What are you doing here?' I've been in Barbara Windor's house for just a few minutes.
"I'm sitting down with a cup of tea and a biscuit with my friend of three decades. I'm taken aback, but I can't show it. When I arrived, she greeted me with a hug, as one of her closest friends.
"Barbara was my "TV mum" on 'EastEnders' and is hilariously funny and vivacious, with a rapier wit - we've always had a giggle, on and off set. But now she clearly has no idea who I am."
The 55-year-old star, who revealed Barbara's husband Scott has a "memory board" in their living room to remind her of details about herself, is delving into the heartbreak of Alzheimer's disease for his latest documentary.
He added: "I'll be honest - it was an emotional roller coaster and their stories often brought tears to my eyes.
"It's impossible for me to walk in their shoes. But by spending time with them and their carers - generally their loved ones - I've tried to gain a greater understanding of how they cope with this devastating disease."
Ross also revealed how he had been visiting 82-year-old Barbara - who played 'EastEnders' icon Peggy Mitchell - regularly before the coronavirus lockdown, and he was stunned by the way her health has deteriorated with her condition.
He explained: "Due to her condition, Barbara didn't take part in the film.
"I see her as often as I can - every couple of months before the lockdown - and the deterioration in her condition has been shocking and to those of us close to her, deeply upsetting."
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