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The Duchess of Sussex celebrated her birthday in style with a two-tiered cake dedicated to one of her favourite pastimes - mahjong.

On Tuesday, Montecito-based Meghan marked her 45th birthday and thanked her followers 'for the birthday love' alongside a photograph of herself jumping into an outdoor pool.

But it wasn't just her Instagram followers sending well wishes: her close friend and fashion designer Tracy Robbins also posted a picture of the Duchess's birthday cake alongside a series of sweet photographs of the pair to mark the occasion.

'Happy birthday to my partner in crime,' she wrote on her Instagram Stories, adding, 'Love doing life with you one bam bird at a time. Love you @meghan.'

The bam bird refers to a tile in mahjong, the popular strategy mind-sport thought to have originated in 19th-century China, where players take turns drawing and discarding tiles, trying to form four sets of three, which Meghan has long enjoyed with a group of close friends, including Tracy, known as the 'Maj Squad'.

Alongside a picture of the cake, which featured 'Meghan' in gold icing, was a photograph of the Duchess blowing out the candles while wearing a wide-brimmed straw hat and her £4,145 Logan Hollowell Queen Emerald Cut Cuban Choker.

Among the other black-and-white images were a picture of a group of friends playing the game, one of Tracy and Meghan at dinner, and another of the pair sipping cocktails.

Meghan has repeatedly revealed her love of mahjong, and in the first series of her lifestyle show, With Love, Meghan, the mother-of-two welcomed Tracy, cosmetics entrepreneur Victoria Jackson and literary agent Jennifer Rudolph Walsh to play while enjoying tacos and cocktails.

The Duchess of Sussex celebrated her 45th birthday on Tuesday - and shared footage of the day on Instagram

Last year, the Duchess's close friend Vicky Tsai, the founder of Tatcha skincare, shed light on Meghan and Harry's hobbies, revealing both enjoy playing mahjong and have taken up pickleball – an increasingly popular paddle sport that combines elements of tennis, badminton and ping-pong.

Speaking to People magazine, she said: 'She's really creative and curious. She enjoys things that you wouldn't expect – like mahjong.

'She's constantly trying to pull me into her weekly mahjong group. And she and Harry are pretty passionate about pickleball. They are trying to convince me to join the group!'

Earlier this summer in June, Meghan added a new member to her 'Maj Squad' – Kelly McKee Zajfen.

Kelly, the Alliance of Moms co-founder – a non-profit that provides support to pregnant and parenting youth in LA's foster care system, joined the Duchess, whom she has been friends with for 20 years, for a game in the sunshine.

Taking to Instagram, Kelly, a former model, shared a picture of herself playing the game outdoors with cocktails, before thanking 'M & T' in the caption, a reference to Meghan and Tracy.

She captioned the picture: 'Ugh, oh. Another one has been taken by the Maj bug. That being me.

'A perfect day spent with my ladies and having some much needed mama time. Thanks M & T. Now back to the babes and obsessing over my next game.'

Tracy Robbins shared a selection of pictures from the special occasion, including Meghan's cake

Tracy then shared the picture to her Stories, writing: 'You are a natural. Love you. Miss you already.'

It comes after Meghan posted a new clip of her dancing to a happy birthday song earlier this week.

The Duchess posted a series of videos from the day on Instagram, showing her bopping to the music and laughing as she and Prince Harry put paper hats on their two dogs, Pula and Mamma Mia.

Her lifestyle brand As Ever also congratulated the mother-of-two with a snap of Meghan wearing a Céline shirt and white Anine Bing 'Brie' jeans.

The company's social media post also included a throwback photo of a young Meghan sporting pigtails and a white turtleneck, seated in what looks to be her childhood bedroom.

The brand wrote: 'Happy birthday to our founder, @meghan. Lighting No. 084 to celebrate!'

The caption referenced a candle sold by the brand, which appeared alongside other As Ever products in one of a quartet of photos posted to celebrate Meghan's special day.