Harper Beckham, 12, shows off matching tattoo with sister-in-law Nicola Peltz

David and Victoria Beckham's youngest Harper Seven marked her 12th birthday on Monday, and the tributes from her doting family flooded Instagram in celebration of her special day.

Harper's sister-in-law Nicola Peltz, who married Brooklyn Beckham in a $3 million oceanfront wedding ceremony in April last year, was amongst the tween's loved ones to celebrate her birthday on social media. Taking to IG, the actress shared a gallery of sisterly snaps with the youngest Beckham, giving an insight into their close relationship.

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"Happy birthday to my baby sis Harper 7," penned Nicola. "You are the most amazing girl I am so lucky to have you in my life. I love you more than you even know! (Can we always match forever?)" 

One photo in Nicola's gallery, which showed the duo rocking matching butterfly tattoos, sparked a divided opinion amongst fans. In the snap, Nicola sported a dainty butterfly tattoo on the small of her back, while Harper revealed her matching ink on her ribcage.

While it seems most likely the sisters were playing around with water-based transfer tattoos, fans were left confused in the comments of Nicola's post.

"Surely a 12 year does not have a real tattoo," wrote one fan, as another wrote: "Probably a stupid question. But is that a real tattoo on Harper?"

Adding to the debate, another chimed in: "Harper is far too young for a tattoo," while a fourth fan wrote: "LOVE that you're both inked."

Given Nicola's penchant for Y2K fashion and Harper's love for It-girl trends, the pair probably jumped on the transfer tattoo bandwagon that has been circulating on TikTok recently - but it wouldn't be a total surprise if Harper chose to get inked later in life.

Harper's brothers Brooklyn, Romeo and Cruz have all been inked just like their dad David. Paying tribute to their star-studded oceanfront nuptials, Brooklyn got a romantic 'Married' inking shortly after his wedding to Nicola.

The detailed tattoo, written in elegant cursive handwriting, was an addition to the 95+ tattoos he already had on his body.

MORE: Adorable Harper Beckham takes after mum Victoria in personal family videos