William has led birthday well-wishes, writing on social media: “To the most incredible wife and mother. The strength you’ve shown over the last year has been remarkable. George, Charlotte, Louis and I are so proud of you.”
The pair married in 2011 and have had three children together, the second in line to the throne Prince George, Princess Charlotte and Prince Louis.
But while the princess has lived a very public life since she joined The Firm, she had a very full time as a relative unknown. This is her pre-royal story.
William and Kate, while dating, watch England v Italy at the Six Nations in 2007
David Davies / PA
Who was Kate before marriage to Prince William?
Her family has gentry ties but is not of royal stock
Catherine Elizabeth Middleton was born on January 9, 1982, in Reading but attended an English language nursery school in Jordan – where the family lived while her father worked for British Airways.
Michael Middleton worked as a flight dispatcher and has aristocratic heritage while his wife and Kate’s mother Carole can trace her family tree back to the Queen Mother.
Kate was the oldest of three, her sister Pippa was born in 1983 and brother James was born in 1987. The former has three children and James has one.
The Middletons made a fortune in the party business
Kate was five when her parents left the airline industry and started on a new venture, making party bags. Party Pieces quickly became profitable and paid for the three children to attend the prestigious Marlborough College, according to the Independent.
Kate is said to have found life tough at the independent boarding school, says the Mirror.
The Princess of Wales’s uncle, Gary Goldsmith
David Mirzoeff / PA Archive
Gary Goldsmith claims his niece was ‘common’ before meeting William
Kate had the nickname of “Squeak” growing up, which owed its origin to a pair of pet guinea pigs that she and Pippa owned as children.
“There was one called Pip and one called Squeak, so my sister was called Pip and I was Squeak,” she later said on a visit to her old school.
She took a cool gap year but had a tough decision over university
Kate could have started at St Andrews University in 2000 but, to somewhat discredit her uncle’s claim that she is not posh, took a gap year to Chile with Raleigh International.
During her late teens, she helped her parents with the party bag business as a salesperson and also modelled for the catalogue.
At university, she studied psychology in a joint honours before choosing to focus solely on art history, while she also worked part-time as a waitress.
William and Kate have been together for more than 20 years
Will Warr / Kensington Palace / PA
William made a beeline for her at a party
Kate led an active social life, co-founding a drinking club and also becoming part of a social group called The Glossy Posse, according to Royals at War.
The pair were said to have been in a relationship since 2003, having been friends for most of their time while studying.
They broke up… and got back together
Mr Jobson said in the book that William had shocked the Middleton family by cancelling plans with them in early 2007, with the pair then agreeing to spend time apart.
“We did split up for a bit, but that was just, you know, we were both very young,” William is quoted as saying in a Marca article. “It was at university, and we were both finding ourselves as such and being different characters.”
Catherine Middleton (R), her mother Carole and sister Pippa arrive at The Goring Hotel after visiting Westminster Abbey on April 28, 2011
Christopher Furlong / Getty Images
Pre-marriage, she lived with her sister, Pippa
Post-university, Kate pursued a career in buying and marketing in London.
The pair on their wedding day
Stefan Rousseau / PA
The pair married in 2011 and the rest is history
And, of course, Kate and William tied the knot on April 23, 2011.
Three children later, the family is gearing up to enjoy Kate’s 43rd birthday celebrations.
William will hit that birthday himself in June, being six months’ younger than his wife.