The Peaky Blinders actress told “very, very few people” about her diagnosis and carried on with her charity work just a few weeks before her death aged 52.
Watch: Cillian Murphy leads tributes to the late Helen McCrory
Speaking on BBC’s Today programme Ms Cracknell said: “Helen wanted to be very private about her illness and I understand why. When you live in the public spotlight you have to find space to protect the things that are just for you.
“Very, very few people knew, and I only did because we were planning to transfer a show to Broadway and we had to cancel that because she was undergoing treatment. We were sworn to secrecy.
“Her need to be fully alive and be committed and to take things incredibly seriously, such as her family and charity work, defined her last few years for her as much as ever.”
Ms Cracknell added that the Harry Potter star faced up to cancer “with a level of bravery and humour that was completely extraordinary”.
“It was a very remarkable thing,” she said.
Ms McCrory selflessly appeared on Good Morning Britain with husband Damian Lewis to promote the Prince’s Trust just six weeks before her death.
Concerned presenter Kate Garraway asked Ms McCrory if she was “alright” due to her “croaky voice”.
Shortly after the exchange Mr Lewis took over speaking for the couple.
On Friday, Mr Lewis broke the tragic news that his wife had died peacefully at home.
The couple, who married in 2007, had a daughter Manon, born in 2006, and son Gulliver, born in 2007.
In a message posted on social media, Lewis said: “I’m heartbroken to announce that after an heroic battle with cancer, the beautiful and mighty woman that is Helen McCrory has died peacefully at home, surrounded by a wave of love from friends and family.”
Ms McCrory, who was awarded the OBE for services to drama in 2017, was best known for playing fearsome matriarch Polly in crime drama Peaky Blinders but also had a critically acclaimed stage career winning plaudits for National Theatre roles in productions of Medea and Terence Rattigan’s post war drama The Deep Blue Sea.
Her Peaky Blinders co-star Cillian Murphy paid tribute, saying: “I am broken-hearted to lose such a dear friend.
“Helen was a beautiful, caring, funny, compassionate human being.
“She was also a gifted actor – fearless and magnificent. She elevated and made humane every scene, every character she played.
“It was a privilege to have worked with this brilliant woman, to have shared so many laughs over the years.
“I will dearly miss my pal. My love and thoughts are with Damian and her family.”
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