Sarah, Duchess of York, has been diagnosed with skin cancer, just six months after being treated for breast cancer.
She was diagnosed with malignant melanoma, a form of skin cancer, after having several moles removed - with one of those identified as being cancerous.
A spokesman for the duchess, 64, said she remained in "good spirits" despite the diagnosis.
She is due to undergo further investigations to ensure the cancer has been caught in the early stages, the spokesman added.
"Following her diagnosis with an early form of breast cancer this summer, Sarah, Duchess of York has now been diagnosed with malignant melanoma," her spokesman 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 spokesman said the duchess wanted to express her gratitude to the medical team - believed to be from King Edward VII Hospital in London - who had supported her through the process.
He said the duchess's experience also underlined "the importance of checking the size, shape, colour and texture and emergence of new moles that can be a sign of melanoma".
Duchess 'proud of mastectomy'
Last year, the duchess, the former wife of Prince Andrew, Duke of York, underwent an eight-hour single mastectomy operation and reconstruction after discovering she had an early form of breast cancer during a routine mammogram.
She previously said she had no symptoms and almost missed her appointment until her sister convinced her to go.
In a TV interview in December, she said she was "proud" of her mastectomy and described it as a "badge of office".
She also described the moment she decided to have her breast removed as she drove away from the Royal Free Hospital in Hampstead, north London, and began searching for information about the disease online.
The news of her skin cancer diagnosis comes after it was announced that the King is to attend hospital next week to be treated for an enlarged prostate.
What is malignant melanoma?
Malignant melanoma is a type of skin cancer that can spread to other areas of the body.
According to the NHS, the main cause of melanoma is ultraviolet light, which comes from the sun, as well as from sunbeds.
Factors such as age, a family history of skin cancer, and having pale skin or a large number of moles can increase your chances of developing melanoma.
A new mole or a change in an existing mole may be signs of melanoma, as well as large moles, or those with uneven shapes, or a mixture of colours.
The NHS advises people to contact their GP if they notice a new mole or changes to existing moles, including if one becomes itchy, painful or inflamed.
People who notice a dark area under a nail that has not been caused by an injury should also contact their GP, according to the NHS.