"Romeo who? I can't stop laughing right now, genius!" the fashion designer captioned the snap.
The photo of her 10-year-old had been photoshopped to style him with the fashion maestro's signature sunglasses, high collar and tied back white hair.
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Romeo is no stranger to the fashion world – he featured in the Burberry spring/summer ad campaign.
Recent figures revealed that his appearance helped the British brand increase sales by 13%.
The second son of David and Victoria Beckham, made his modelling debut at the beginning of this year, following reports he was headhunted by Burberry chief creative officer, Christopher Bailey, last December.
The schoolboy appeared alongside top models Cara Delevingne, Edie Campbell and Charlie France in the spring/summer shoot.
Even so, reports have suggested that it was the young Beckham brand that triggered the "exceptional" response to the British fashion house in the first quarter of 2013.
''The Beckhams are showbiz royalty so it's no surprise that Romeo's first ad campaign has been a roaring success.
''With his dad's good looks and mum's amazing dress sense, he's the perfect model. Other brands will be fighting to sign him up,” a fashion insider told The Sun.
Romeo follows his designer mother , Victoria, into the fashion sphere, an area he appears clearly familiar with.
"He had a real opinion, he was so involved in what he was wearing," Burberry boss Christopher Bailey reported at the time.
According to Christopher, Romeo "stole the show" with his infectious enthusiasm, captured in the shots taken by world famous photographer, Mario Testino.
The result was, "in what remained an uneven trading environment… an exceptional consumer response to spring/summer 2013," Burberry reported.
In particular, the ad campaign and catwalk shows were seen to have made a "record reach and engagement".
Richard Hunter, head of equities at Hargreaves Lansdown Stockbrokers, admitted it was an "impressive start to the year" for the brand.