The Duke and Duchess of Sussex shared a 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 on Friday 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.

'We will climb this one with you'

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."

Following Kate's announcement, her brother James Middleton posted a photo 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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How the newspapers have reacted to Kate's announcement

World leaders pay tribute to 'courageous' princess

Prime Minister Rishi Sunak has been joined by other world leaders in sharing a message of support for Kate and the royals.

In a statement shared on X, he wrote: "The Princess of Wales has the love and support of the whole country as she continues her recovery.

"She has shown tremendous bravery with her statement today... I know I speak for the whole country in wishing her a full and speedy recovery and look forward to seeing her back in action when she's ready."

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".

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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".

Vaughan Gething, first minister of Wales, said that "all of our thoughts are with you as you continue your treatment".

Northern Ireland's leaders, Michelle O'Neill and Emma Little-Pengelly, have both sent messages of support on social media.

Sinn Fein's Ms O'Neill said she was "very sorry" to hear the news and sent her best wishes.

The DUP's Ms Little-Pengelly said Kate will be "in the thoughts and prayers of so many across Northern Ireland".

Meanwhile, US President Joe Biden wrote on X that he and his wife Jill "join millions around the world in praying for your full recovery, Princess Kate".

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

French President Emmanuel Macron wrote on X: "In this difficult period you are going through, Brigitte and I wish you a full recovery.

"Your strength and resilience inspire us all."

Canadian Prime Minister Justin Trudeau wrote: "On behalf of Canadians, I'm sending my support as she undergoes treatment. We're all wishing her a swift recovery."

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Kate's uncle Gary Goldsmith, who recently appeared on the revived Celebrity Big Brother, shared a statement on X 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, 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.

It comes as England football manager Gareth Southgate gave a brief statement after the Princess of Wales' announcement, sharing his "best wishes to her and her family".

Mr Southgate has a close bond with the family as Prince William is president of the Football Association.

The Three Lions boss, who was speaking ahead of tonight's match against Brazil, said: "It was a remarkably dignified statement. We have a close relationship with the family so we're very upset to hear the news. Hopefully everything goes well."

'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.

Oscar-winning actress Catherine Zeta-Jones shared a picture of Kate on Instagram, writing: "Wales and the World is with you. HRH Princess of Wales. Love to you always."

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... 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."

Fellow Love Island star Zara McDermott, who now fronts BBC Three documentaries, also worked alongside Kate last year as part of the royal's Shaping Us campaign - highlighting the importance of early years development.

"Sending HRH Princess of Wales so much strength and love during this time," McDermott said in an Instagram story.

Strictly Come Dancing star Amy Dowden said the news from Kate had "personally hit me hard", after she was diagnosed with stage three breast cancer and received chemotherapy treatment.

She said: "I was lucky enough to meet the Princess of Wales during my treatment who was so kind, supportive and generous of time.

"Sending all my well wishes with treatment ahead and as always to all those affected by cancer."

US actress and X-Men star Olivia Munn, who last week revealed her breast cancer diagnosis in the hope it will help others to "find comfort, inspiration and support on their own journey", also commented on Kate's social media video.

"Thank you for showing what it's like to fight with grace and determination for yourself and for your family. Wishing you all the best," she said.

There was also an apology from Hollywood actress Blake Lively, who had seemingly mocked Kate after she issued a personal apology for manipulating a family photograph, sparking conspiracy theories about her whereabouts.

Referencing a now-deleted Instagram post, Lively said: "I made a silly post around the 'photoshop fails' frenzy, and oh man, that post has me mortified today. I'm sorry. Sending love and well wishes to all, always."