The Queen "disapproved" of Kate Middleton's "frivolous displays of wealth" before marrying Prince William, a royal biographer claims.

Author Katie Nicholls says Her Majesty found Kate's lavish London lifestyle "unpalatable."

KATE MIDDLETON BRINGS HER OWN SPECIAL ITEM TO ELEMENTARY SCHOOL'S SHOW-AND-TELL

The royal author wrote in her 2010 biography "William and Harry": "If [Kate] was not with William at Balmoral then the couple were skiing or holidaying on Mustique.

Kate Middleton (right) originally endured a rocky start with Queen Elizabeth II.

Kate Middleton (right) originally endured a rocky start with Queen Elizabeth II. (Getty)

"Kate was there so often the press dubbed her 'Queen of Mustique,' a title that had previously belonged to Princess Margaret."

A source told the royal expert that: “Swanning from one five-star holiday resort to another is not the prerequisite for a young woman possibly destined to be Queen.”

The Queen was unsettled by Kate’s exotic holidays, but also her prominence on the London club scene as Britain entered a recession in 2008.

The author wrote: "Britain was now in recession and such frivolous displays of wealth were unpalatable to The Queen.”

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Duchess of Cambridge Kate Middleton

Duchess of Cambridge Kate Middleton (Splash)

It’s reported that Kate Middleton was “stung by the Queen’s criticism," and despite being advised by Clarence House not to publicly comment, the now-Duchess claimed to be working for her parent’s company as a photographer.

A black-and-white photo of Kate appeared on the website but was taken down shortly after.

Katie said: "It was deemed a step too far and within weeks it had been removed."

Stepping in with some advice, it’s claimed the Queen steered Kate into more suitable roles.

The biography says: "The Queen had quietly suggested that Kate affiliate herself with a charity and, by September, she was involved with Starlight, which works with seriously and terminally ill children."

Kate Middleton and Prince William pose for a photo with their three children, George (right), Charlotte (middle) and Louis.

Kate Middleton and Prince William pose for a photo with their three children, George (right), Charlotte (middle) and Louis. (AP)

Prince William and Kate Middleton met in 2001 at St. Andrew's, and are thought to have started dating in 2003.

After briefly splitting in 2007, while skiing at the Swiss resort of Zermatt, the couple got engaged in 2010, marrying the following year.

The couple is now parents to Prince George, five, Princess Charlotte, three, and Princes Louis, 10-months-old.

This article originally appeared in The Sun.