Ms James, 40, known as Bowel Babe online after campaigning to raise awareness of bowel cancer, has raised more than £3 million after setting up a Just Giving page.
The former headteacher was diagnosed with bowel cancer in 2016 and has kept her more than 500,000 Instagram followers up to date with her treatments.
On Monday, the mother-of-two announced she had been moved to hospice at home care, adding that she did not know “how long I’ve got left”.
She urged people to give to her donation page, which echoes her social media handle Bowelbabe, to raise funds for lifesaving cancer research and to support campaigns to raise awareness of the disease.
In a personal tweet, William and Kate said: “Every now and then, someone captures the heart of the nation with their zest for life & tenacious desire to give back to society.
“@bowelbabe is one of those special people. Her tireless efforts to raise awareness of bowel cancer & end the stigma of treatment are inspiring.
“We are so sad to hear her recent update but pleased to support the @bowelbabef, which will benefit the @royalmarsdenNHS among others.
“Deborah, our thoughts are with you, your family and your friends. Thank you for giving hope to so many who are living with cancer. W & C.”
James has been treated at the Royal Marsden hospital, of which William is patron, and it is one of the beneficiaries of her fund.
Charities say the outpouring of donations reflected a wider surge in interest in bowel cancer, which around 268,000 people in the UK have been diagnosed with, according to Bowel Cancer UK.
They have thanked Ms James for being so open about the treatment and signs of her bowel cancer, which can at times be shied away from as symptoms concern people's toilet habits.
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James was diagnosed with bowel cancer in 2016 and has since kept her more than 500,000 Instagram followers up to date with her treatments.
On Tuesday, ITV News Entertainment Reporter Rishi Davda looked at the work Deborah James has done to help others suffering and raise awareness of bowel cancer's symptoms
Now receiving end-of-life care at her parents home in Woking, the mother-of-two has revealed the devastating impact of her illness on her children, 14-year-old Hugo and 12-year-old Eloise.
“It’s been hideous telling my children. We have had a string of emotional conversations that have escalated very quickly from supportive care to end-of-life care," she told The Times on Wednesday. “My husband Sebastien has been incredible, he has dropped everything and is with me 24/7. “My first thought was (that) I don’t want my children to see me like this. I didn’t think I would be able to speak to them without crying, but I’d love one last cuddle with them.”
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Ms James, who has campaigned over the past five years for more awareness of bowel cancer symptoms and funding for research, said she had always wanted to set up a fundraiser.
She has thanked the public for their outpouring of generosity, saying she feels "utterly loved".
In her final episode of the podcast shared on Tuesday, titled "Deborah James' Last Dance", she said her liver had stopped working over the past six months, which she said has been "really rough".
She said doctors told her treatment has now become "fruitless" due to her liver not functioning, but quickly joked: "She says drinking a glass of Champagne."
What are the symptoms of bowel cancer?
According to the NHS, the three main symptoms of bowel cancer are:
persistent blood in your poo – that happens for no obvious reason or is associated with a change in bowel habit
a persistent change in your bowel habit – which is usually having to poo more and your poo may also become more runny
persistent lower, bloating or discomfort – that's always caused by eating and may be associated with loss of appetite and weight
However, the NHS says most people with these symptoms do not have bowel cancer. Other health problems can cause similar symptoms such as a change in diet or haemorrhoids.