Sarah Ferguson, the Duchess of York, has been diagnosed with malignant melanoma, a form of skin cancer. She is said to be in "shock" but in "good spirits".
The cancer diagnosis was discovered during a check-up with the Duchess of York's dermatologist.
Her spokesman said: "Following her diagnosis with an early form of breast cancer this summer, Sarah, Duchess of York has now been diagnosed with malignant melanoma.
"Her dermatologist asked that several moles be removed and analysed at the same time as the Duchess was undergoing reconstructive surgery following her mastectomy, and one of these has been identified as cancerous.
"She is undergoing further investigations to ensure that this has been caught in the early stages."
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Last year, the Duchess sadly discovered she had breast cancer, following a routine mammogram screening. She went on to have a single mastectomy at King Edward VII Hospital in London, a private clinic used by senior royals.
Taking to Instagram, she thanked those who have shared their support following the news. "Naturally another cancer diagnosis has been a shock but I’m in good spirits and grateful for the many messages of love and support.
"I believe my experience underlines the importance of checking the size, shape, colour texture, and emergence of new moles that can be a sign of melanoma and urge anyone who is reading this to be diligent," she said.
The 64-year-old was married to the Duke of York, Prince Andrew, for 10 years before they divorced in 1996.
They continue to share a home at Royal Lodge - a property owned by the Crown Estate at Windsor Great Park in Berkshire.