The Ella & Co founder, 33, revealed that it was his puppy Nala's first birthday and shared a fun boomerang with his beloved dogs.
WATCH: James Middleton celebrates puppy's "special day"
James wrote: "Today is a very special day! It's Nala's 1st Birthday.
"We celebrated with Granny Ella and Dad Zulu, and thank you for the confetti card @boomf.
"She is now officially an adult... Although it's been just a year, I cannot imagine life without her in the pack."
James introduced pup Nala last May
He wrote on Instagram at the time: "Introducing Nala Middleton. She is the daughter of Zulu & granddaughter of Ella. I cannot wait to share many adventures with her and the rest of the pack."
James has become an uncle again to Pippa's second child
It's been a week of celebrations for the Middletons after Pippa, 37, gave birth to a daughter on Monday 15 March.
The author and columnist has named her baby Grace Elizabeth Jane.
"Mother and baby are doing well," a family source told HELLO! on Monday. "She's perfect, everyone is overjoyed at such a happy arrival."
Back in 2015, James celebrated the birth of his niece Charlotte with a bottle of champagne, writing on Instagram at the time: "A little pink champagne to celebrate!"
James and his fiancée Alizee
The Ella & Co founder had been due to marry fiancée Alizee Thevenet last year, but the couple had to postpone their nuptials twice amid the coronavirus pandemic.
James popped the question to the French financial analyst in October 2019 last year after dating for around 12 months.
James has been delighting fans with pictures and videos of his beloved dogs in recent months, including his own rendition of the Sea Shanty TikTok craze.
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