Appearing on Damian Barr's Literary Salon, the screenwriter said that he actually planned for the show to be eight episodes long, with a final episode that would have revisited the remaining characters on the show in their later lives.
"It could've been eight episodes long, and there would've been an extra flatmate, and he would've had adventures," he revealed during the chat. "But I was offered four episodes, and that's fine. Everything that I would've done kind of compacted inwards."
WATCH: Have you caught up on all episodes of It's a Sin?
Russell explained that though he was able to bump up the series from four episodes to five, there was "always meant" to be another episode set in the present day.
"It was never written, so it doesn't exist, but it was kind of budgeted for," he said of the episode. "We'd catch up with Jill at the age of 55 and she's still working in mental and sexual health. It's too long a story to describe, but you get the feeling that she's trapped in that world, actually."
The original ending would have explored Jill's later life
Viewers would have seen Jill, who is based on one of Russell's real-life friends, "going on cruise ships and to conference centres and singing songs on the West End with all her mates".
One trip in particular would have led her back to Ritchie's home on the Isle of Wight, which Russell said "she's never been back to since" his death. "She decides to go, she goes back to the Isle of Wight to meet that family. That's why there was a sister there, in Ritchie's household."
Viewers would have learned about Valerie a bit more
In a dark twist of fate, Jill would have visited Ritchie's ageing mother in a care-home and uncover the "sexual abuse at the heart of the Tozer household and [learned] how Valerie ended up like she did," he revealed.
As for Roscoe, he said that the episode would have seen Jill reconnect with him and learn that he had sadly contracted HIV in middle age. "You know, 50 years old and he's got the virus having escaped it all those years," he said.
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