The brother of the late Princess Diana has expressed his support for Kate Middleton amid her cancer battle.

One day after the Princess of Wales revealed in a video released by Kensington Palace that she had been diagnosed with cancer and is undergoing treatment, Charles Spencer, her husband Prince William's uncle, praised her on social media.

Alongside a screenshot of Kate in the clip, the ninth Earl Spencer, wrote on Instagram, "Incredible poise and strength."

In recording the video, Diana's daughter-in-law had broken her silence about her health journey amid weeks of public speculation online and in the media about her well-being. The rumors began after Kensington Palace announced in January that Kate had undergone abdominal surgery and would be taking a break from her royal duties.

In the video, which BBC Studios filmed at Windsor March 20, Kate revealed that she was diagnosed with cancer after undergoing the operation, which she described as "major."

"At the time, it was thought that my condition was non-cancerous," she added. "The surgery was successful. However, tests after the operation found cancer had been present. My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment."

Kate, who shares kids Prince George, 10, Princess Charlotte, 8, and Prince Louis, 5, with William, added, "This of course came as a huge shock, and William and I have been doing everything we can to process and manage this privately for the sake of our young family." The screenshot of her video that Charles posted included a caption of part of her statement that read, "to process and manage this privately."

The 59-year-old had recently compared the media scrutiny of Kate to that of his late sister—mother of both William and Prince Harry—prior to her death.

When asked about his thoughts on the recent rumors about Kate, Charles told BBC's Sunday with Laura Kuenssberg, in an interview released March 17, "I do worry about what happened to the truth."

Diana, ex-wife of King Charles III and one of the most beloved philanthropists in the world, died in 1997 at age 36 in a car crash in Paris after being pursued on the road by paparazzi. William and Harry, then 15 and 12 years old respectively, were not with her at the time of the accident.

"I think it was more dangerous back in the day," Charles said about the media scrutiny of his sister. "If I look back to '97 and Diana's death, I think that was so shocking, the circumstance of her death was so shocking, that it did make the industry that supports the paparazzi really consider more carefully what it could and couldn't do. Not because they had a moral judgment, but because it was unacceptable to the public."

Charles is not the only one of Kate and William's family members to publicly share their well-wishes for the princess following her announcement of her cancer diagnosis. Her brother, James Middleton, The King and wife Queen Camilla and Harry and wife Meghan Markle have all expressed their support, as have a slew of celebrities and world leaders. Read their messages below:

The Beverly Hills, 90210 alum, who has herself been battling cancer for years, wrote on Instagram, "I admire your strength thru the endless onslught you've been under while going through cancer."

On March 22, 2024, Kensington Palace released a video of Kate Middleton revealing that she is undergoing treatment for cancer, which was discovered after she had abdominal surgery in January.

"Wales and the World is with you HRH Princess of Wales," Zeta-Jones, who was born in Wales and was made a Commander of the British Empire (CBE) by now-King Charles III in 2011, wrote on Instagram. "Love to you always."

The Newsroom alum, who revealed March 13 she has been battling breast cancer, commented on Kensington Palace's Instagram video of Kate, "Thank you for showing what it's like to fight with grace and determination for yourself and your family. Wishing you all the best."

"We are praying for your full & complete recovery & for strength of mind, body & spirit for you & your entire family," the Rizzoli & Isles alum commented on Kensington Palace's video of Kate. "Thank you for your beautiful spirit & courage."

The media personality, fiancée of Amazon founder Jeff Bezos, commented on the post as well, writing, "Sending love."

"My thoughts are with the Princess of Wales, Prince of Wales, the Royal Family and in particular her three children at this difficult time," he said in a statement on X. "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."

He added, "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."

Speaking at a press briefing following news of Kate's health battle, she said their thoughts are with the princess "and her family members and friends during this incredibly difficult time," adding, "certainly we wish her a full recovery."

"Over the years, we have climbed many mountains together," Kate's brother wrote on Instagram, alongside a childhood pic of the two, after she revealed her health diagnosis. "As a family, we will climb this one with you too."

The ninth Earl Spencer, brother of the late Princess Diana and Prince William and Prince Harry's uncle, wrote on Instagram, "Incredible poise and strength."

The Duke and Duchess of Sussex, who stepped back as senior royals in 2020 and live in California, said in a statement to NBC News, "We wish health and healing for Kate and the family and hope they are able to do so privately and in peace."

A Buckingham Palace spokesperson said the King, who shared his own cancer diagnosis in February, is "so proud of Catherine for her courage in speaking as she did."

In fact, Charles has "remained in the closest contact with his beloved daughter-in-law throughout the past weeks," the rep told NBC News, adding that both he and Camilla "will continue to offer their love and support to the whole family through this difficult time."

"You are brave," President Joe Biden's wife wrote on X, "and we love you."

"On behalf of Canadians, I’m sending my support as she undergoes treatment," he wrote on X. "We’re all wishing her a swift recovery."

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