Harry and Meghan shared the message of support for their sister-in-law in a statement, saying: "We wish health and healing for Kate and the family, and hope they are able to do so privately and in peace."

The princess announced earlier this evening that she has been diagnosed with cancer and is undergoing preventative chemotherapy.

In a personal video, the future queen said she had wanted time to explain to her three children, George, Charlotte and Louis, "to reassure them that I am going to be okay", following weeks of speculation about her health.

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Following her announcement, her brother James Middleton posted his own tribute with a picture of the two of them together as children, saying the family would rally round.

"Over the years, we have climbed many mountains together. As a family, we will climb this one with you too," he wrote on Instagram.

James is the younger brother of Kate and their sister, Pippa.

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King Charles, who is also currently being treated for cancer, shared a message of support for his daughter-in-law, with Buckingham Palace saying: "His Majesty is so proud of Catherine for her courage in speaking as she did.

"Following their time in hospital together, His Majesty has remained in the closest contact with his beloved daughter-in-law throughout the past weeks.

"Both Their Majesties will continue to offer their love and support to the whole family through this difficult time."

Kate's family are among thousands around the world sending their love to the royal.

Prime minister praises 'tremendous bravery'

Prime Minister Rishi Sunak led the messages from the political sphere, praising the royal's "tremendous bravery" and saying she has the "support of the whole country".

Home Secretary James Cleverly wished Kate "a speedy and complete recovery and privacy and calm while she does", while Chancellor Jeremy Hunt described her as "courageous".

Labour leader Sir Keir Starmer said the princess has "the love and support of not just her whole family, but the whole nation too" during this "distressing time".

Former prime minister Boris Johnson wished her "all possible strength" and a "full and rapid recovery," while his successor Liz Truss said her "thoughts are with the Princess of Wales and her family at this very difficult time".

Humza Yousaf, the first minister of Scotland, said he was "deeply saddened" to hear the news and is "praying for her swift recovery."

And in the US, First Lady Jill Biden simply posted: "You are brave, and we love you."

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Kate's uncle Gary Goldsmith, who recently appeared on the revived Celebrity Big Brother, shared a statement on X, formerly Twitter, saying: "I hope this draws a line over the continued speculation and horrible conspiracies. Let's give Kate, William & the children time and show some love back."

He also acknowledged an interview he has given to The Times, which is set to run tomorrow, saying he was "deeply upset" about the timing.

"As many will have seen, I am featured in Saturday's 'Times Magazine'. This interview and shoot was done over a week ago and went to print before I was aware of the sad news regarding my niece Kate," he said.

'The princess is a stomper. A real good egg'

Celebrities who have met the princess were also among the thousands of well-wishers showing support online.

Author and broadcaster Giovanna Fletcher, who hosted Kate on her parenting podcast Happy Mum, Happy Baby, in 2020, said "The Princess of Wales has always led with dignity, grace and compassion. Working alongside her always gives the greatest lessons in how to care. How to listen. How to 'human'.

"I'm thinking of our future queen and hope she can now be left with nothing but everyone's good wishes as she continues her treatment and surrounds herself with the love of her family."

Meanwhile, former Love Island contestant Dr Alex George, now a TV doctor campaigning on mental health issues who hosted a panel discussion with William and Kate last year, said the princess had "left a real impression" when they met for World Mental Health Day.

"I have met so many people who talk about mental health over the years, I have come to learn who talks the talk, and who walks the walk," he said. "The princess is a stomper. A real good egg...

"Just remember, be kind. You never know what challenges someone is facing, or the battles they are trying to overcome. You got this, Your Royal Highness."