Kate, Duchess of Cambridge, 40, chose a belted monochrome polka-dot dress by Alessandra Rich for the occasion, which she paired with a brown flat-brimmed fascinator, decorated with delicate white flowers. She completed the look with drop pearl earrings and neutral make-up.
Prince William kept to tradition, wearing a black top hat and tails as well as an ivory waistcoat and blue patterned tie.
The Duke and Duchess made their first appearance at the race series on Friday, joining other members of the royal family who have been present at the races since they began on Tuesday.
Prince Charles and his wife Camilla have been in attendance, as well as Princess Beatrice and her husband Edoardo Mapelli Mozzi, Sophie, Countess of Wessex, and Zara and Mike Tindall.
Queen Elizabeth II will not attend this year’s races, despite having two horses running, due to ongoing mobility issues.
On Tuesday, Sheikh Hamdan bin Mohammed, Crown Prince of Dubai, was in attendance. Wearing a sharp grey, shin-length morning coat with matching tie, top hat and darker grey trousers, Sheikh Hamdan shook hands with Camilla, Duchess of Cornwall, as he received the trophy for Coroebus's win in the St James's Palace Stakes.
Royal Ascot is Britain's most valuable horse racing meet, and runs until Saturday. Thursday’s Ladies' Day is thought of as the most glamourous day, with guests dressing to the nines for the occasion.
Hats, fascinators and elaborate headgear galore sit atop fashionably dressed women who attend day three of Britain's most valuable horse racing meet.
It was referred to as Ladies' Day in 1823, after an anonymous poet described Thursday at the races as such, saying "when the women, like angels, look sweetly divine", or so the story goes.
Royal Ascot doesn't officially call it that, though. "Vibrant, celebratory and steeped in tradition, the third day of Royal Ascot, colloquially known as Ladies' Day, is a day to see and be seen," reads a description on its website.
On behalf of the royal family, Zara Tindall, the Princess Royal's daughter and a celebrated equestrian, wore a stylish full-brim green hat by Justine Bradley-Hill, along with a white, puffy sleeved coat dress by Laura Green.
Sophie, the Countess of Wessex, was also in attendance on Thursday, wearing full floral attire. Her ankle-length dress sported a V-shaped neckline and she paired it with a bright pink fascinator.