Kate Middleton, who celebrates her 42nd birthday this Tuesday, was rich before joining the royal family.

As of 2023, Celebrity Net Worth (CNW) estimated the Princess of Wales' net worth to be around $10 million.

While she's seen her fortune grow since marrying Prince William, Middleton was already part of a well-off family.

Her parents, Carole and Michael, are reportedly self-made millionaires, thanks to the success of Party Pieces, their mail-order party supply and decoration company.

The company, which was valued at approximately $40 million in 2013, was sold to entrepreneur James Sinclair last year for an undisclosed sum, the BBC reported.

Princess Kate's involvement with Party Pieces suggested she may have had a stake in the family business, according to Cosmopolitan.

Kate Middleton
(Photo : CHRIS JACKSON/POOL/AFP via Getty Images)
Britain's Catherine, Duchess of Cambridge reacts as she arrives ahead of the World Premiere of the James Bond 007 film "No Time to Die" at the Royal Albert Hall in west London on September 28, 2021.

Carole revealed to SheerLuxe that her eldest daughter played a role in developing the company's first birthday and baby category.

This successful venture reportedly allowed the Middletons to afford private school education for Kate and her siblings, as well as luxurious vacations and attendance at high-profile events, according to Hello! magazine.

But the Middleton family's wealth is not solely tied to Party Pieces.

CNW said that trust funds established over a century ago have benefited multiple generations of the Middleton family.

Before her royal life, Kate and her sister Pippa lived in a Chelsea, London, apartment purchased by their parents in 2002 for £780,000 ($990,000 today).

The sisters reportedly moved out after Kate's wedding to Prince William in 2011. The property sold for £1.88 million ($2.4 million) in 2019.

Today, Middleton and Prince William are believed to share their finances. Multiple reports and royal experts, including Katie Nicholl and Ingrid Seward, said that the members of the British royal family typically do not sign prenuptial agreements before they get married.

Prince William, Kate Middleton
(Photo : GLYN KIRK/AFP via Getty Images)

The Prince of Wales is estimated by CNW to be worth $100 million as of 2023.

Prince William has inherited wealth from various sources. He received a substantial trust fund from the Queen Mother and an additional $10 million after taxes from Princess Diana that was split with his brother, Prince Harry.

Both Prince William and Princess Kate also receive income each year for their roles as working royals.

While the exact figure is unclear, campaign group Republic claimed that Prince William was effectively paid more than £127,000 ($161,000) an hour by British taxpayers last year after he carried out just 172 engagements.

Prince William also benefits from the Duchy of Cornwall, a portfolio with assets totaling £1.2 billion ($1.5 billion) that he took over from his father King Charles in 2022. The duchy reportedly pays him an income of over £22 million ($28 million) a year.

Meanwhile, Princess Kate received a special birthday message from King Charles and Queen Camilla Monday.

The royal family's official page on X, formerly Twitter, posted a photo of Middleton from King Charles' coronation last year, along with the message: "Wishing The Princess of Wales a very happy birthday today!"

According to People, Middleton is expected to celebrate her 42nd birthday with her husband and their three children, Prince George, Princess Charlotte and Prince Louis, privately this weekend.