James Middleton said he was "surrounded by family" on his special day after vowing to "climb this mountain" with Princess Kate.
The Princess of Wales's younger brother celebrated his 37th birthday today, and took to Instagram to mark the occasion.
James shared a rare photograph of his baby boy Inigo, whom he shares with his wife Alizee Thevenet.
He captioned the post: "Matching bérets to celebrate my birthday.
Kate was diagnosed with a form of cancer last month
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"Surrounded by family, friends and of course my dogs."
Inigo, who was born in October 2023, wore a matching béret to his father, who had covered his son's face with a white heart emoji in the photograph.
This post marked James's return to his personal Instagram after vowing to "climb this mountain" with his sister Kate.
The Princess of Wales, 42, announced via video last month that she had been diagnosed with a form of cancer.
James was Kate's first family member to publicly wish his sister well.
Taking to Instagram at the time, he wrote: "Over the years, we have climbed many mountains together.
"As a family, we will climb this one with you too."
The father-of-one previously broke his silence on his separate Instagram account, James & Ella, named after one of his many dogs.
James Middleton posted this childhood image of himself and Kate on InstagramInstagram / James MiddletonLATEST ROYAL NEWS:
Kate shared her cancer diagnosis with the world via videoPA On National Puppy Day, James shared an adorable video of a puppy with several other dogs on the grounds of his Berkshire residence.
James captioned the post: "Happy National Puppy Day!
"There's a minefield of information out there on how you should prepare taking a puppy home for the first time.
"With a pack of six dogs and multiple litters under my belt, check out the link in my bio for my best advice on welcoming your new puppy home."