Princess Diana’s brother is supporting her daughter-in-law, Catherine. Charles Spencer praised his niece-in-law the Princess of Wales on social media following the release of her personal message on Friday.

Reposting Her Royal Highness’ video on X (formerly Twitter),Prince William and Prince Harry’s maternal uncle wrote: “Incredible strength and poise.”

In her video, Catherine revealed that when she underwent her abdominal surgery in January, it was thought that her condition was non-cancerous, however tests after her operation found that cancer had been present and she is now in the early stages of preventative chemotherapy treatment.

The Princess’ younger brother, James Middleton, penned a moving message for his sister Catherine after her announcement. “Over the years, we have climbed many mountains together. As a family, we will climb this one with you too ⛰️❤️,” he captioned a throwback photo of the two of them.

A Buckingham Palace spokesperson has said that King Charles, who was diagnosed with a form of cancer this year, is “so proud of Catherine for her courage in speaking as she did.”

His Majesty and the Princess were both at The London Clinic in January. After their time in the hospital, the monarch has “remained in the closest contact with his beloved daughter-in-law throughout the past weeks.” The spokesperson said that both King Charles and Queen Camilla “will continue to offer their love and support to the whole family through this difficult time.”

Prince Harry and Meghan Markle have also issued a statement, wishing “health and healing” for their sister-in-law. The Duke and Duchess of Sussex said: “We wish health and healing for Kate and the family, and hope they are able to do so privately and in peace.”