Prince William is always perfectly polished and poised when it comes to royal engagements.
The future King consistently seems to be on top form on his public outings and is a consummate professional when it comes to more serious outings.
But on one occasion, his demeanour slipped ever so slightly when he fought to keep his eyes open at an annual Westminster Abbey event.
The slip came in April 2018 when William made a surprise appearance at the Anzac Day Service of Commemoration and Thanksgiving at Westminster Abbey alongside his brother Prince Harry and then-future sister-in-law Meghan Markle.
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William was caught on camera almost nodding off as he listened to the service - but with good reason.
Just two days earlier, he and Princess Catherine had welcomed their third child, little Prince Louis, at the Lindo Wing at St. Mary’s Hospital in London.
No doubt operating on just a few hours' sleep, the royal appeared to drift off a few times, then waking back up with numerous blinks - a sure sign of a newborn parent.
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Louis arrived on 23 April 2018 and returned home to Kensington Palace that very day. He made his public debut in his mother's arms on the steps of the Lindo Wing just seven hours after he was born.
William and Kate announced their third child’s full name as Prince Louis Arthur Charles on April 27, 2018 - four days after his birth.
The meaning behind Prince Louis's names
Just like their two older children, Prince George and Princess Charlotte, the couple gave their son a traditional name with plenty of links to the royal family.
Louis is a nod to the Duke of Edinburgh's uncle, Lord Louis Mountbatten, and the Duke's maternal grandfather, Prince Louis Alexander of Battenberg. Prince George also has Louis as a middle name, just like his father William. The name, which is French and German in origin, means "renowned warrior".
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Arthur, which had been a popular choice with the bookies, is another of Prince William's middle names, as well as King Charles'. It was also a middle name of the Queen's father, King George VI.
Charles, meanwhile, is a clear nod to Prince Louis' paternal grandfather, whose full name is Charles Philip Arthur George.
The statement confirming Louis' birth read: "Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs. The baby weighs 8lbs 7oz. The Duke of Cambridge was present for the birth. Her Royal Highness and her child are both doing well."
It continued: "The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news."
Princess Kate lets slip family nickname for Prince Louis
Just last week, the princess revealed her very precious nickname for her youngest during an engagement in Northern Ireland.
The royal stepped out alongside her husband in Belfast, and when stopping to talk to a group of young school children, the name was dropped.
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One of them quizzed Princess Catherine on what her children's names were, and she replied: "Thank you for asking. I have George and Charlotte, and the little one is called Louis."
Fans were delighted to hear the Princess refer to Louis as the "little one", considering he is already eight years old. But clearly, he is still the baby of the family.
In the past, the royals have revealed that they also call Louis 'Lou Lou' or 'Lou Bug'.
Louis isn't the only child given a nickname, as in the past Princess Catherine has referred to her daughter as "Lottie," a shortened version of Charlotte.
Their eldest, Prince George, has a pun-tastic nickname, meanwhile. Reportedly, his parents took to calling him "PG", standing for Prince George. From there, William and Catherine playfully took the next step and began calling him "PG Tips" or simply "Tips," after the classic British tea brand.