Kate Middleton Sparkles in an Emerald Gown for King Charles' Private 75th Birthday Party

Prince William and Princess Kate sent the King a special message for his banner birthday

Kate Middleton was glowing in green for King Charles’ birthday!

On Tuesday, the Princess of Wales was seen leaving her father-in-law’s birthday bash with Prince William at the wheel of the car. King Charles turned 75 on Tuesday and celebrated with a private party for family and friends at Clarence House following a busy day of royal engagements.

Although Princess Kate was only seen riding in the car, eagle-eye fans identified her dress as Needle & Thread's Alicia gown in emerald.

Other royal family members spotted heading home from the event included Princess Beatrice; Zara and Mike Tindall; David Armstrong-Jones, 2nd Earl of Snowdon; Lady Sarah Chatto and the Duke and Duchess of Gloucester.

While Buckingham Palace is the most iconic residence of the British royal family in London, King Charles and Queen Camilla don’t live there. A $460 million renovation is currently underway at the hub of the monarchy’s operations, and Charles and Camilla remain based at Clarence House near St. James’ Palace, where they have lived for years.

Related: Kate Middleton and Prince William Mark King Charles' 75th Birthday with Sweet Family Photos

Earlier in the day, Prince William and Princess Kate, both 41, wished King Charles a happy birthday on social media with a sweet post that included family photos.

And Kate was on the go again on Wednesday, when she brought together experts from across the world to a conference held by her Royal Foundation Centre for Early Childhood at the Design Museum in central London.

"It is time we understood that building a healthier world means nurturing the foundations that support our children — everything from the systems that govern early care through to our attitudes to those raising the next generation and the support they receive," Kate said at the event.

King Charles began his birthday with an important royal duty: the launch of the Coronation Food Project. The King and Queen Camilla, 76, toured the South Oxfordshire Food and Education Alliance to see how the new venture will “bridge the gap between food waste and food need across all four nations of the United Kingdom, helping people and helping the planet," the palace said.

The Coronation Food Project is an offshoot of the King Charles III Charitable Fund and got its start with a $1.2 million fund supported by a personal donation from the King in December 2022. Moving forward, the Coronation Food Project will help food networks across the U.K. reuse greater amounts of surplus food.

Later on Tuesday afternoon, King Charles stepped out solo to host a reception celebrating midwives and nurses working in the U.K. at Buckingham Palace. The event was timed to the 75th anniversary of the National Health Service (NHS) this year. The reception welcomed about 400 nurses and midwives from diverse backgrounds and cultures, plus some of the 150,000 nurses and midwives from countries including India, the Philippines, Poland and Kenya who are currently working in the U.K., as well as reps from the International Nursing and Midwifery Associations.

During the festive reception, the NHS Choir surprised the King by singing “Happy Birthday.” The rousing rendition marked at least the fourth time King Charles heard the classic tune in his honor in two days, following the performances of the song at the Highgrove Gardens tea party on Monday, at the Coronation Food Project on Tuesday and later at Buckingham Palace by the Irish Guards Band.

Related: Find Out What King Charles Was Called During Rendition of 'Happy Birthday' (Hint: It's Not 'King')

As seen in a video shared on X by Richard Palmer of the Daily Express from the Coronation Food Project stop, supporters, staff and volunteers joined their voices to sing “Happy Birthday” to the King — although that's not what they called him during the tune!

When the time came to state Charles’ name, the group sang "Happy birthday, Your Majesty," using the correct formal address for the monarch. King Charles raised his eyebrows at the “Your Majesty” mention, in what appeared to be a self-deprecating reaction to his royal role as sovereign.

According to the royal family’s official website, which has yet to be updated in full following the death of Queen Elizabeth in September 2022, "there are no obligatory codes of behaviour when meeting The Queen or a member of the Royal Family." The Royal.UK website outlines that the traditional form is a neck bow from the head for men and a small curtsy for women, though some people prefer to simply shake hands.

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As for greetings, Royal U.K. states, “On presentation to The Queen, the correct formal address is 'Your Majesty' and subsequently 'Ma'am,' pronounced with a short 'a,' as in 'jam'. "

While King Charles would be referred to as “Sir” on second reference as a male member of the royal family, the “Your Majesty” title can also be used. It would also be appropriate to call Queen Camilla “Your Majesty” because she is the Queen.

Meanwhile, royal family members like Prince William and Princess Kate should technically be addressed as “Your Royal Highness” and subsequently “Sir” or “Ma’am” from there, the royal family website states.

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