Kate Middleton Dress
Kate Middleton attends a reception at Australia's Parliament House in Canberra April 24.Reuters

Kate Middleton has apparently disappointed, though unintentionally, American fashion designer Ralph Lauren, whose collection the Duchess has often sported.

The ace designer is said to be upset over Kate's absence at a gala charity dinner hosted by Prince William at Windsor Castle on Tuesday night.

The dinner was held to celebrate the work of The Royal Marsden, the specialist cancer treatment hospital in London of which Prince William is a patron since 2007.

Lauren, who is funding an entire new breast cancer research centre at the hospital's Chelsea site, had reportedly sponsored the star-studded royal dinner as well.

William hosted the event without Kate Middleton, who supposedly stayed back to look after their nine-month-old son, Prince George.

However, the 74-year-old Lauren was not so convinced when he came to know that Kate would not attend the event.

"Ralph Lauren was furious when he found out less than six weeks ago that Kate would not be there," a source told Mail Online.

"He considered pulling out but was told by his PR advisers that it would look terrible. The company thought they were getting Kate, the most famous clothes horse in the world, and also a runway show at the castle," the source added.

But representatives of the veteran designer insisted that he has "only ever been enthusiastic about attending the event."

A Kensington Palace spokesperson defended the Duchess of Cambridge's absence at the dinner where A-list celebrities like Emma Watson, Kate Moss and Cate Blanchett were the star attractions.

"The Duke and Duchess regularly undertake separate engagements in support of the charities with which they are involved," the spokesperson said.

William apologises about Kate

The Duke of Cambridge was quick to apologise for the absence of his wife as soon as he met Ralph Lauren at the dinner gala.

"I'm sorry my wife's not here, you probably would far rather you saw my wife," the 31-year-old Duke told Lauren and his wife Ricky Anne Loew-Beer.

To this, Lauren replied saying that he was excited about meeting the Duke, whose mother, Princess Diana, he knew through their common work interest of fighting cancer.