Pippa Middleton’s friends have shared insights into their fiercely committed relationship with Kate Middleton.

The Princess of Wales, 42, revealed last week that she was starting preventive chemotherapy for an undisclosed type of cancer.

Shortly thereafter, Kate’s brother James Middleton shared an unseen childhood photo of him and the princess on Instagram, along with a heartfelt message.

“Together we have overcome countless challenges over the years. As a family, we are committed to supporting you through this as well,” he said.

Although Pippa, 40, is rarely seen on social media, her close circle of friends has provided insight into the close relationship between her and Kate.

A source close to Pippa said: “The three siblings are very close… Pippa is not only a sister but a best friend that she can count on.”

They went on to tell The Times: “They were extremely loyal to each other.”

Pippa and Kate both have three children of similar ages.

The Princess of Wales and Prince William tied the knot in 2011 and share children Prince George, 10, Princess Charlotte, 8, and Prince Louis, 5

Meanwhile, Pippa married hedge fund manager James Matthews in 2017 and has children Arthur, five, Grace, three, and Rose.

Kate and her sister lived together in a Chelsea flat in their 20s, a sign of their close relationship.

The 40-year-old also served as bridesmaid at the wedding of the Prince and Princess of Wales, which took place on the world stage.

Pippa now lives in Adelaide Cottage on the Windsor estate, just a stone’s throw from the princess’ home.