The Harry Potter actor might look like the iconic actor with layers of make-up, brown contact lenses and a tan that would make a Love Islander look pale, but Isaacs told Sky News' Backstage Podcast that Cary Grant was really just a persona created by Archibald Alec Leach, whose life began with a miserable childhood in Bristol.

"I didn't want to play Cary Grant - he played Cary Grant, he struggled to play Cary Grant, he found it very difficult," Isaacs said.

"The reason [the series is] called Archie is he just wasn't that man, everything that he was on-screen, he was the opposite most of the time.

"Off-screen he could be that, but that wasn't who he was on the inside at all, he was the very opposite of suave and smooth - he was jagged and troubled and in pain."

Isaacs said it was that flawed character he wanted to explore - not the beloved Grant.

"The idea of stepping into the shoes of the world's most attractive superstar, you know, you'd have to be professionally suicidal to try to do that," he laughed.

"But reading Jeff [Pope]'s script and also diving into it, it just felt like, oh no, there was a man who was incredibly damaged and that is the kind of stuff actors love doing."

To play the part, Isaacs did his homework, watching Grant's films and trying to find material of him giving interviews in order to find his speaking voice.

But he says it soon became clear there was no such material available.

"I couldn't find an interview, I just couldn't find any chat show or anything he'd ever done, or radio interview," he recalled.

"After a bunch of detective work, I found an interview that looked like a transcript and I tracked the guy down, and he was a student who'd interviewed Cary Grant in the last year of his life.

"He'd written to him thinking he might get some written answers, and instead he got an answer back saying 'call on Saturday morning, we'll have a chat'.

"He went to his university radio department to talk to him and the first thing Cary Grant says when he comes on, he goes 'you're not recording this are you? I don't want you to'.

"So [the student] signalled to his friend to stop recording, and when they finished the interview an hour later, his mate went 'well I did, obviously', and he'd never played it to anybody in 40 years, and he was very suspicious of me when I got in touch with him - out of respect, because he was a huge Cary Grant fan - and I begged him, and he very generously shared it with me."

Read more entertainment news:
Taylor Swift left devastated by death of fan ahead of show
Sean 'Diddy' Combs settles lawsuit after abuse allegation
Paapa Essiedu on his 'rambunctious opposition' to typecasting

Isaacs described hearing Grant as the "final key" to unlocking the part.

"I thought, okay, now I've heard Archie Leach, now there's someone I understand," he said.

"It doesn't sound like he does in the films, not just accent-wise but character-wise. There's some irritation, there's some insecurity, I heard a real man is what I heard.

"Apart from all the outside stuff, the walk, and the angle of his head and all the rest of it and his bandy knees, that was the final piece of the outside stuff.

"There's the outside stuff, but really, the inside stuff is what matters.

"What we want to do is play what these people were, what they were feeling.

"For Cary Grant, it was all the terrible, open, festering wounds of his childhood, all the abandonment and abuse and his sense that he only was valued by whether people found him attractive."

Isaacs's co-star Laura Aikman plays Grant's fourth wife Dyan Cannon and admitted she had something of an easier time when it came to researching her role.

"Jason was quite jealous that I could just ring Dyan," she laughed.

"But yes, I had loads of interviews, which is - like Jason was saying - more helpful than the films, because the films are more of a polished performance, and I found just watching Dyan over and over again, I got so obsessed.

"But the thing that sort of keyed me into her, I guess, was her laugh - she's got this big infectious laugh, and she's quite famous for it, and I feel like once I got that, I kind of got Dyan in a way, and her energy."

Aikman said the period costume and styling also played their part in getting her into character.

"I think it was really helpful because I'm not like Dyan like that - I'm in 'walk the dog' clothes all the time - so that really helped me feel like her," she explained.

"And it was great for me and Jason because actually we had two hours in the chair together every day because we both had so much make-up, so we got to know each other pretty quick."

Isaacs agreed.

"I mean, I've worn sweatpants since COVID - I don't think I've worn anything that isn't made of elastic! So, yes, both of us looked and felt so far from who we were," he said.

There's no doubt the physical transformation is impressive - Isaacs isn't easily recognisable either in the promotional shots or the show itself.

"There's not much of me left to view," he admitted.

"I was covered in mahogany fake tan the entire time, luckily, we were in Liverpool, so that didn't stick out!

"It was odd when it came off at the end of the day, me going, 'oh Jesus, that's me'."

Click to subscribe to Backstage wherever you get your podcasts

Now the show is about to air it seems the pair have mixed feelings about audiences seeing them as Cary and Dyan.

"I enjoy living in their world so much I sort of don't really want to share it with anyone," Aikman admitted.

"Also because it'll be over, but obviously so many people worked so hard on it, so it's nice that everyone will finally get to see it."

"For me, I let go of things," said Isaacs.

"I've no idea whether anybody's going to watch it, whether everybody's going to watch it, whether they'll like it or hate it - personally to take this job at all I had to decide early on that I was going to ignore the billion people who went, 'well, it's all very well, but he's no Cary Grant'.

"I could have written those reviews myself, but it's all about the process for me at this point.

"I think it's got a lot to tell us about today, about coming through [mobile phones] are a million people whose lives look perfect, and we feel less than perfect by comparison.

"And it's a reminder not to do that and to deal with the baggage of your childhood. I think it's a great story, but I've let it go now - it's not ours any more."

Archie is out on ITVX on 23 November.