Over the past few months, fans have seen Cleaver's character Eileen Grimshaw embark on a relationship with firefighter Paul Kershaw (Hirst), whose wife Lesley suffers from early onset Alzheimer's disease.
Most recently, Paul agreed to move Lesley (Judy Holt) into a care home for a trial period, having finally conceded that he was finding it too difficult to look after her.
Hirst today (April 19) told Lorraine of playing Paul: "It's a massive responsibility. Right from the beginning, the creative team were really careful that they knew it would be a sensational storyline, but they wanted to do it justice.
"They've been in constant contact with the Alzheimer's Society, and our scripts are checked and verified by them - in terms of credibility and being realistic and true to the issue."
He continued: "With viewers who come up and see you, the ones who make a judgement are the ones who have absolutely no experience or understanding of dementia. The fans who have some experience of people living with dementia are absolutely positive, and they want Eileen and Paul to find some kind of happiness.
"People are writing to us on a daily basis. Interestingly, the Alzheimer's Society wanted to know where the hope would come in our story. It's really difficult because it is bleak and it is brutal, but I think the hope lies in [the fact that] people do find mechanisms to cope. However dysfunctional people think Eileen and Paul are with Lesley, actually they are functioning."
Cleaver added that she has also been pleased with the reaction to the ongoing plot.
She said: "It's been lovely, actually - the response. It's quite controversial, the story, but people affected with Alzheimer's in their life really get it and really understand it. There was concern as to how people would respond to this."
The pair were recently spotted filming a major turning point in the storyline, which is expected to air next month.
Cleaver explained: "There's lots of twists and turns coming up, and what we're filming at the moment is all very exciting. We can't speak too much about that. We'll have to see what happens."
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