While Prince William marks his 42nd birthday out of the public eye, his father King Charles is stepping out for another thrilling day at the Royal Ascot horse races.

King Charles and Queen Camilla returned to the Ascot Racecourse in Berkshire on June 21 but not before the monarch marked his eldest son and heir’s birthday on social media. The royal family’s official X and Instagram accounts celebrated the Prince of Wales’ milestone with a black-and-white throwback photo showing the father and son when William was just a baby.

“Happy Birthday to The Prince of Wales!” the sweet snap was captioned, complete with a party horn emoji.

While the Queen, 76, has attended all four days of Royal Ascot so far this year, King Charles, 75, skipped the outing on Wednesday, holding audiences at Buckingham Palace instead.

Once again, the royal couple led the Royal Procession that kicks off each day’s event at 2 p.m. local time. They rode in a horse-drawn carriage onto the racecourse grounds joined by family friends Lord and Lady Bamford.

The second carriage in the four-coach parade carried Princess Beatrice and her husband, Edoardo Mapelli Mozzi. Although Princess Beatrice, 35, attended Royal Ascot on June 19, she did not take part in the Royal Procession that day. They were joined by Lord Frederik Windsor (the son of Prince and Princess Michael of Kent) and his wife, actress Sophie Winkleman.

The riders in the procession dressed to impress, adhering to Royal Ascot’s strict dress code requirements for the Royal Enclosure.

King Charles and other men sported a morning suit and top hat in the approved colors — black, grey or navy suits with a black or grey hat — with a waistcoat and necktie (“patterns of a patriotic nature, for example, a national flag, are acceptable,” according to the guidelines).

Meanwhile, ladies attending the horse races in the Royal Enclosure must sport hats with a minimum base of four inches paired with a skirt, dress, trouser suit or jumpsuit following the dress code.

After races were underway, Princess Beatrice presented the award to the winning team of the Duke of Edinburgh Stakes. The race was renamed in 1991 to honor Prince Philip, Beatrice’s grandfather who died in 2021.

The title of Duke of Edinburgh was given to Prince Edward in 2023 by his brother King Charles.

Royal Ascot is a longstanding highlight on the royal family’s calendar, and the late Queen Elizabeth was a huge supporter of the equestrian event. In fact, 24 of her racehorses won at the prestigious horse races through the years.

This year has seen many members of the royal family attend, including Princess Eugenie, Princess Anne, Peter Phillips, Zara Tindall, Prince Edward, Sophie Duchess of Edinburgh and Lady Gabriella Kingston in her second outing with the royals since her husband’s death earlier this year.

Although Prince William didn’t spend his birthday at Royal Ascot, he attended the event on June 19. After riding in the Royal Procession, the Prince of Wales caught up with his in-laws, Carole and Michael Middleton, who made their first public appearance since their daughter Kate Middleton publicly announced her cancer diagnosis. At one point, Prince William even assisted his mother-in-law when her heel got caught in the grass, causing her foot to slip out of her shoe! They laughed as William held Carole’s arm so she could reach down and fix the minor wardrobe malfunction.

Princess Kate, 42, did not attend Royal Ascot despite her appearance at Trooping the Colour on June 15. The outing for King Charles’ birthday parade marked her first time joining the royals at an event since Christmas as she continues her treatment, but it did not signal a return to public life.

“She has been doing what’s right for her and recovering privately at home. She is dealing with it the best she can,” a source close to the royal household tells PEOPLE exclusively in this week’s cover story.