Sarah, Duchess of York feared she wouldn't see her grandchildren grow up following her breast cancer diagnosis earlier this year.
The 64-year-old author, who underwent a single mastectomy in June, appeared on Thursday's episode of Loose Women to talk about her experiences and to support the show's inaugural Don't Skip Your Screening campaign.
Joining presenters Christine Lampard, Coleen Nolan and Brenda Edwards on the panel, Sarah said: "I'm very grateful to the Royal Free Hospital and the NHS because they have got this extraordinary dye that they put through your arm, and it can actually really detect the shadows."
She continued: "It's quite extraordinary, 18 months before it wasn't there. So, it had come on from the last mammogram to this mammogram.
"The drive from the Royal Free Hospital, I'll never forget because of course your mind goes into, 'oh my goodness, I've got to have a mastectomy' and you look it up and it's all terrifying and 'this is what's going to happen' and then, 'I'm not going to see my grandchildren grow up'. That's what goes through your head."
Sarah is grandmother to Princess Beatrice's two-year-old daughter Sienna and Princess Eugenie's sons, August, two, and five-month-old Ernest.
The Duchess is incredibly close to her daughters and often shares anecdotes about them and her grandchildren on her podcast series Tea Talks With The Duchess & Sarah.
She told the Loose Women panel that she nearly missed her mammogram but went after her sister Jane's insistence.
"I almost missed the screening appointment that saved my life," she revealed, "I couldn't face a journey into London on a hot day this summer and it was only my sister Jane's insistence that I went, that persuaded me."
Sarah added: "My cancer was completely symptom-free – I never found a lump and did not feel ill. My experience underlines the vital importance of getting screened when you're called in."
The Duchess underwent an eight-hour single mastectomy operation on her left breast in June, as well as reconstructive surgery.
She said she is "proud" to support the campaign, which is being backed by NHS England, to encourage other women to attend the appointments when they are invited.
Charity Breast Cancer Now said it is "extremely grateful" that the show is "shining a bright spotlight on breast screening" and "highlighting the important issue of tackling the shortfall in women having breast screening caused by the Covid-19 pandemic".
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