The esteemed actress, who played Polly in the BBC's gangster drama, passed away in April this year at just 52 years old, after battling cancer.
And now, Cillian Murphy, who leads the Peaky Blinders as Tommy Shelby, has spoken candidly about what filming has been like on the award-winning series without Helen's electrifying talent.
"It's desperately sad," the 45-year-old said on Irish radio station Today FM. "Sad for all of us who knew her, and the people who were close to her and the fans."
"She was like the matriarch of Peaky Blinders, and the person I was closest to. The Polly and Tommy scenes were some of my favourite scenes in the show. It's desperately sad. We're all still trying to come to terms with it."
Cillian has previously spoken warmly about his close friendship with Helen while on set, as the pair shared many moments on-screen together.
"Oh, man. She was my closest colleague on Peaky, and one of the finest actors I've ever worked with," he told The Guardian in May.
"Any material, any scenes... she made it special. She could do power and vulnerability, one after the other."
He added that Helen as a person "was just so cool and fun, and had such compassion for everyone she met."
"I was kind of in awe about how she lived her life - the way she balanced her work and her family so beautifully," he said.
Filming on the upcoming series of Peaky Blinders finished in May, following multiple delays due to the coronavirus pandemic.
While Polly was an integral character in the series, it is still to be confirmed how the series will explain her absence.
A release date for Peaky Blinders season six is still yet to be announced.
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