The Princess of Wales' brother James Middleton broke his silence on Kate's cancer diagnosis, RadarOnline.com has learned.
After Kate, 42, revealed in a video message on Friday afternoon that she has been diagnosed with cancer, James, 36, posted a heartfelt message to his sister online.
James took to Instagram shortly to share a sweet message after news of his sister's health made headlines.
The 36-year-old shared a throwback photo of him and Kate along with the caption, "Over the years, we have climbed many mountains together. As a family, we will climb this one with you too."
Support for Kate and the Middleton family poured in from around the world in the post's comment section.
"So much love and respect for your entire family. Princess Catherine is beloved beyond measure," wrote one Instagram user.
"Rooting for her every step of the way, from the USA. She’s brave and she’s a fighter. She will conquer this," commented another.
A third responded, "It must be so comforting for your sister to know she has a wonderful support system in her family. Anyone who’s been touched by cancer in some way knows how it affects the entire family, so I’m sending you all good thoughts and to your sister, healing thoughts."
James' post follows a shocking and emotional video from Kate, in which she explained her recent absence from public life that sparked a plethora of conspiracy theories regarding her health and whereabouts.
The princess revealed she's in the early stages of "preventative chemotherapy" treatments following her abdominal surgery in January.
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While the type of cancer and stage was not disclosed, Kate said the diagnosis came as a "huge shock."
"I wanted to take this opportunity to say thank you, personally, for all the wonderful messages of support and for your understanding whilst I have been recovering from surgery," Kate said in the video.
"It has been an incredibly tough couple of months for our entire family, but I’ve had a fantastic medical team who have taken great care of me, for which I am so grateful."
While at the time of her surgery it was believed that her "condition was non-cancerous," further testing afterward confirmed "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," the princess shared.
Kate noted her husband, Prince William, has been "a great source of comfort and reassurance" during this difficult time.