The couple have survived and thrived through breakups, family bereavements and celebrations, as well as the birth of their three children.
Here we map the key dates in the relationship of the future King and Queen.
Engagement: October 2010
Prince William had made a secret trip by motorbike to see the Queen to collect his late mother’s 18-carat blue sapphire and diamond engagement ring.
On a safari in Africa later that month he carried it in his rucksack, terrified of losing it, and proposed to Kate in a secluded spot near Mount Kenya.
Announcing their engagement, he said: “It is my mother’s engagement ring. It is very special to me and Kate is very special to me now as well. It is only right the two are put together.”
William said in his engagement interview: “When I first met Kate I knew there was something very special about her.”
He spoke about how their relationship developed: “We just spent more time with each other, had a good giggle, had lots of fun and realised we shared the same interests and just had a really good time. She’s got a really naughty sense of humour.”
Wedding: April 2011
On 29th April 2011, William and Kate were married at Westminster Abbey, in a ceremony thought to have been watched by as many as two billion people in more than 180 countries around the world.
The bride wore an intricate ivory gown with lace applique floral detail designed by Sarah Burton of Alexander McQueen, while the groom was dressed in the red tunic of the Irish Guards.
During the service, William told Kate she looked “beautiful” and joked to his father-in-law: “We’re supposed to have just a small family affair”.
Much attention was given to Kate’s sister, Pippa, for her figure-hugging bridesmaid dress, with a Facebook page set up in honour of her derriere.
After the service, the newlyweds travelled in an open-top carriage for the 15-minute journey from Westminster Abbey to Buckingham Palace.
More than a million people lined the procession route as street parties erupted across the nation. An evening do for 300 guests at the Palace, hosted by Charles, followed – with Kate switching into another Sarah Burton gown.
The cost of the wedding was met by the Prince of Wales and the Middletons, but the security bill – with £6.35 million spent on policing – fell to the taxpayer.
July 2013: Prince George born
Prince George was born in the maternity ward at St. Mary’s Hospital Paddington, known as the Lindo Wing.
The Duchess later she was terrified of that first photocall standing in the same spot where Princess Diana and Charles showed off William to the world.
“Everyone had been so supportive and both William and I were really conscious that this was something that everyone was excited about and, you know, we’re hugely grateful for the support that the public had shown us, and actually for us to be able to share that joy and appreciation with the public, I felt was really important,” she said.
May 2015: Princess Charlotte born
Princess Charlotte was born on May 2, and the proud parents showed off their baby girl, again outside of the Lindo Wing.
Royal gun salutes in London’s Hyde Park and at the Tower of London signalled the birth of the new princess.
Princess Charlotte is fourth in line to the throne and the Queen’s fifth great-grandchild.
June 2016: Vogue cover star
The Duchess of Cambridge graced the front page of Vogue‘s 100-year centenary issue. The magazine has previously featured Diana, Princess of Wales, Princess Margaret, the Queen Mother, and the Queen.
The Duchess, photographed by Josh Olins in the Norfolk countryside, appeared dressed casually to reflect her love of the countryside and particularly Norfolk.
She didn’t grant an interview but was involved in selecting pieces for the shoot.
On the cover she is seen wearing a Burberry trench coat and a £293 white jacquard shirt by the same fashion house.
The magazine said it was the “most personal and natural” royal portrait ever undertaken.
May 2017: Pippa’s wedding
Then three-year-old George and two-year-old Charlotte were on their best behaviour as they were ushered into St Mark’s church in the Berkshire village of Englefield for their aunt’s big day.
George wore a white shirt and gold bloomers while his younger sister donned a white tea dress with a peach ribbon around the waist.
April 2018: Prince Louis born
Kate and William welcomed their second son, Prince Louis, on April 23.
“We’re very happy. We’re delighted. Thank you,” the Prince told the press as he, Kate and the newborn left the hospital hours later.
“You’ll find out soon enough,” William teased of the name at the time. “We didn’t keep you waiting too long.”
May 2019: Kate’s Chelsea Flower Show garden
The royal family released a heartwarming clip along with photographs, which show Prince Louis running through the garden, which Kate co-designed.
Prince Louis, Prince George and Princess Charlotte were all pictured enjoying the playful visit to their mother’s garden, ahead of the start of the Chelsea Flower Show.
The RHS Back To Nature garden was an initiative to encourage children to get outdoors and enjoy nature to boost their mental health.
It was co-designed by the Duchess taking inspiration from her own woodland garden at Anmer Hall in Norfolk, where she would stay during the 2020 coronavirus lockdown.
The Duchess even gave the Queen a tour of the garden when she visited the Chelsea Flower Show.
October 2019: Every Mind Matters
Before Megxit, the Princes and their partners broke the internet when the website for a mental health campaign, fronted by the Dukes and Duchesses of Cambridge and Sussex, crashed as people rushed to view its newly-released advert.
Harry, Meghan, William and Kate narrated the short film as they launched the Every Mind Matters initiative, which is aimed at empowering people to manage the early symptoms of poor mental health.
Within minutes of the advert being broadcast, the Every Mind Matters page of the NHS website was down for a short period - believed to be due to the number of people attempting to view the short film.
October 2020: Loss of family pet, Lupo
The Duke and Duchess of Cambridge mourned the loss of their nine-year-old black cocker spaniel Lupo. He was a wedding present from Kate’s brother, James Middleton.
William and Kate said he had been “at the heart of our family”.
In an Instagram post, they wrote: “Very sadly last weekend our dear dog, Lupo, passed away.
“He has been at the heart of our family for the past nine years and we will miss him so much.”
April 2021: Death of Prince Philip
Prince Philip was fond of the couple and was said to have told the Queen, “thank goodness he didn’t give her up” after the couple broke up in the early years of their relationship.
The couple were naturally devastated at his passing but his funeral provided a chance to heal wounds with Prince Harry.
William and Harry were seen putting on a united front at their grandfather’s funeral thanks to a little help from the Duchess of Cambridge.
After the emotional ceremony Kate, who William refers to as the royal family’s “peacekeeper” started chatting animatedly to Harry.
Then, instead of getting into their separate cars, Harry, William and Kate decided to walk back to the castle together.
Though still wearing his face mask, Harry appeared to smile briefly in the direction of Kate, his sister-in-law, as the three strolled together, away from the rest of the family.
Moments later the brothers walked on ahead together, as Kate hung back to talk to Zara Tindall.
A royal source told the Sun: “Harry appeared grateful for the opportunity, and Kate seemed to make a point of letting the brothers walk alone together, having briefly chatted to Harry as well.”