Prince William and Kate Middleton
Prince William pictured with Duchess of Cambridge, Prince George and Princess Charlotte Getty

The Duchess of Cambridge has long been renowned for her sartorial influence, with pretty much everything she wears selling out within hours as part of the so-called 'Kate effect'.

And now Prince Harry's Suits actress girlfriend Meghan Markle isn't too far behind, with many of her ensembles being wildly searched by the masses. When she pitched up to the Invictus Games earlier this month wearing a 'The Husband' shirt by fashion designer friend Misha Nonoo, everyone raised their eyebrows at its poignant name and proceeded to hunt it down online.

But it's a member of Kate Middleton's immediate family that has stolen her style crown, according to a new eBay report.

The royal who has the "biggest spend power" of any of the royal family is the duchess's two-year-old daughter Princess Charlotte, who is blissfully unaware of her impact on the fashion world.

She is already driving the most searches for her outfits of any of her famous family, including her dapper double-breasted blazer aficionado granddad, Prince Charles.

After photos were released from her second birthday on 2 May of her wearing a knitted yellow cardigan form John Lewis, eBay searches went into overdrive and "increased tenfold". The cute item sold out "instantly" and lookalike versions began cropping up everywhere.

Princess Charlotte
Kate Middleton took the snap of birthday girl Princess Charlotte at the family home in Anmer Hall AFP/Getty Images

Similarly, when Charlotte wore a smock dress during the young royal family's tour of Germany in July, there was a six-fold increase after the tot was seen wearing it.

eBay's vice president of trading said: "The Royal Family are hugely popular with British buyers with Her Majesty regularly attracting the attention of shoppers. But it's the youngest generation of royals who really generate the must-have fashion items, and driving a new generation of shopping [behaviour] on eBay," the Daily Mail reports.

Kate – who is currently pregnant with her third child – has still got it in terms of selling power, however. There is still a big spike in searches whenever she wears anything, from a certain pair of skinny jeans to an Alexander McQueen dress. Her most popular piece on eBay among US royal fans was the cobalt blue Saloni dress she wore back in April, while UK fans were more interested in the pink McQueen dress she wore for her sister Pippa Middleton's wedding earlier this year.

Pippa Middleton's wedding
Kate Middleton and Princess Charlotte at Pippa Middleton's wedding AFP/Getty Images