A royal family member has offered rare insight into King Charles III's cancer battle.

Peter Phillips, son of the King's sister Princess Anne and the eldest grandchild of the late Queen Elizabeth II, spoke about his uncle's mindset amid his road to recovery in an on-camera interview released March 24, more than a month after the monarch began treatment.

"He's in good spirits," Peter told Sky News Australia. "I think, ultimately, he's hugely frustrated. He's frustrated that he can't get on and do everything that he wants to be able to do. But he's very pragmatic. He understands that there's a period of time that he really needs to focus on himself."

The 46-year-old, who is visiting Australia as a patron of the charity ISPS Handa—which supports disabled athletes—continued, "But, at the same time, he is always pushing his staff and everybody and his doctors and nurses, to be able to say, 'Actually, can I do this, can I do that?' I think the overriding message would be that he's obviously very keen to get back to a former normality and he's probably frustrated that recovery is taking a little longer than probably he would want it to."

This marks the most detailed comments a royal family member has made about Charles' health battle since Buckingham Palace announced Feb. 5 that the 75-year-old had been diagnosed with an unnamed form of cancer and had that day "commenced a schedule of regular treatments."

On March 21, his wife Queen Camilla told well-wishers in Belfast that her husband was "doing very well" and "was very disappointed he couldn't come" with her on her trip to Northern Island.

The Palace had also said in their statement that while Charles had "been advised by doctors to postpone public-facing duties" amid his treatments, he "will continue to undertake State business and official paperwork as usual." Indeed, the monarch has met with various officials at the Palace over the past few weeks.

Peter's interview with Sky News Australia was recorded before Charles' daughter-in-law Kate Middleton broke her silence about her own health journey since her abdominal surgery in January to reveal in a March 22 video that she herself had been diagnosed with cancer and had also begun treatment.

The Princess of Wales, who shares children Prince George, 10, Princess Charlotte, 8, and Prince Louis, 5, with husband Prince William, added, "William and I have been doing everything we can to process and manage this privately for the sake of our young family."

In his interview, Peter praised his cousin's wife. "She's remarkable in herself," he said. "Her and William make a fantastic team together. Their kids are great and they have the balance of public life and trying to be a parent to three young children, which is always difficult."

Read supportive messages members of the royal family, celebs and world leaders have shared for Kate following her cancer news:

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."