Beatrice, showing off her svelte figure - the result of months of marathon training - looked lovely in a dusky peach draped gold dress. Topping off the polished look was a navy bolero and a netted fascinator.
Her younger sister was equally chic in a beautiful fuschia dress and hat combination.
Matching the Queen's granddaughters for elegance was Princess Haya Bint Al Hussein.
The Middle Eastern royal, a half-sister of King Abdullah of Jordan, is the junior wife of HH Sheikh Mohammed Bin Rashid Al Maktoum, the ruler of Dubai.
An accomplished horsewoman, she has represented Jordan at international showjumping competitions.
Pretty Haya stood out in a vibrant shade of green, teamed with a simple emerald necklace and a wide-brimmed titfer, featuring feathers.
Other racegoers on Thursday included Simon Cowell and a group of friends.
Among them was Sinitta in a silver satin number with matching headgear and Jackie St Claire, who wore a midnight blue dress that contrasted with her oversize giant anemone hat.