Sarah Ferguson has been diagnosed with an aggressive form of skin cancer.
A mole was removed from her body which had been tested as a malignant melanoma, the most serious form of skin cancer.
It is the latest in a series of health battles to hit the Royal Family.
Fergie, 64, was hit with this health scare just six months after she was treated for breast cancer.
Sarah, Duchess of York has been diagnosed with malignant melanoma following the removal of a cancerous mole during treatment for breast cancer
PA
The Duchess of York was today described as "in good spirits" by her spokesperson.
However, it has been reported that she is finding a second cancer diagnosis within six months as "distressing".
Insiders told The Sun: "It has not been an easy time".
Dermatologists raised the alarm after removing several moles from her body while having reconstructive breast surgery last year.
Tests which came through just days after Christmas revealed one mole was malignant.
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Sarah Ferguson, Duchess of York
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A spokesperson for the Duchess said: "Her dermatologist asked that several moles were 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.
"Clearly, another diagnosis so soon after treatment for breast cancer has been distressing but the duchess remains in good spirits.
The duchess wants to thank the entire medical team which has supported her, particularly her dermatologist whose vigilance ensured the illness was detected when it was.
"She believes her experience underlines the importance of checking the size, shape, colour and texture and emergence of new moles that can be a sign of melanoma."
It comes after the King's medical announcement about his enlarged prostate has led to a surge in men going to get their prostate checked.
Dr Laurence Gerlis told GB News he is "delighted" that the King's news has encouraged men to go and get checked out.
He said: "Men aren't very good at going to the doctor and they're not very good at talking about their private parts.
"So I'm delighted people are talking about it now."
Sarah Ferguson attending the Sandringham Christmas Day service
Reuters
The announcement comes as Kate, the Princess of Wales remains in hospital after having abdominal surgery.
The 42-year-old will not be able to return to work until April while Prince William has cleared his diary to be by her side at The London Clinic in Marylebone.
She is expected to remain in hospital for two weeks before being sent home to recuperate and will not return to front line duties until after Easter, on doctor's orders.
Meanwhile The King will have an operation this week and be on light duties for up to a month.