Kate Middleton and Prince William were present as Prince Charles's 70th birthday party on Wednesday, after a busy day of royal engagements.
The celebrations included a lunchtime at Buckingham Palace with all the royal family, including Meghan Markle and Prince Harry, who expect their first baby.
But Duke and Duchess of Cambridge had their own special reason to celebrate, as Prince Charles's birthday marks a milestone in their relationship.
At the age of 60 of the Prince of Wales's birthday party in 2008, Kate and William were in a very different place in their relationship.
Although they had not yet engaged, the couple had known each other for seven years at this point and the nation was hopeful about a royal marriage.
Their relationship was often in the lights and at one point per year, in 2007, they were split up briefly.
Later, Prince William explained in their engagement interview that "only a separate time" would be needed but that he was "working out for a better" and they joined months later.
In Prince Charles's 60th anniversary Bash at the Highgrove Estate, the couple had two years away from engaging and the Duke had hit friendship with his father-in-law in the future.
Kate and William met in 2001 when both came to St Andrews University, but they have explained in the past, and it took them time to get right to know each other.
So, when they came to a 60-year-old Charles 60 birthday party in 2008, the couple had already come very far in their relationship and engagement.
Prince William did not stop the question until 2010, during a trip to Kenya.
However, fast on to 2018 and their lives are very different.
The couple now are parents of Prince George, five, Princess, three, and Prince Louis, seven months.
Their family has also expanded with the arrival of Prince Harry's wife, Meghan Markle – who is now pregnant with his / her first child.
At the age of 70 Prince Charles's birthday portrait released last week, the different things of the royal family and how popular they have come out have been further tested – thanks to Kate and Meghan.
Within that period, the younger generation of royalties has certainly changed things, with Duchess Sussex bringing a very modern update to the royal family.
Both Duchess are the sponsors of charities who are close to their hearts and often only attend royal debates.
However, there are also rare occasions when Prince William and Catherine work with Meghan and Prince Harry to campaign with each other, something that has won the son's nickname four & # 39; to them.
Despite their close bond, Prince William and Prince Harry will report soon sharing their court; at Kensington Palace to create two separate offices.
With a few months so busy in advance and William takes more responsibilities like the King in the future, it seems that it could be a time to erase what is called "son of four".
The news was reported for the first time by the Sunday Times, and is said to be due to marriage, family life and changing roles.
The brothers have formed their four sons; with their wives, creating incredible power at the front of the modern Royal Family.
But the pressure of the monarchy, the marriage and their serious roles present new challenges to the Duke of Cambridge and Sussex.