So what does one wear to her first Ascot outing?
She was the ideal balance of formal and fashionable in a attractive white lace dress from Dolce & Gabbana.
The Duchess of Cambridge, Kate Middleton, is rumored to be pregnant again only a year after her youngest daughter Princess Charlotte was born.
Prince William's father, Prince Charles, and his wife, Camilla, also signed the book, and the Clarence House Twitter account posted their message online.
The Duke and Duchess of Cambridge braved an untimely downpour as they made their debut appearance at Royal Ascot.
Hillsborough Castle is the official residence of the British royal family when they are in Northern Ireland, and the home of the Secretary of State since the early 1970s. She adds as Kate Middleton takes care of the guests "She kept on asking if we had enough to eat"; she ensures the Duchess that dinner kept on coming. Mrs. "I told him my first cousin actually registered the birth of his two babies at the palace - he thought that was lovely", she said.
The Duchess, who teamed her £3,450 dress from Dolce and Gabbana, with a woven gold Jane Taylor hat. She described her visits with her family as among her "most cherished" memories.
The ground at Ascot remains soft for the second day of the royal meeting, making the ground ride slow, the clerk of the course said.
Chris Stickels said: "It's not as wet out there on the track as it was yesterday but the going will still be quite testing".
Her Majesty, who is a well-known horse breeder, often has several of her own studs racing in the competition.
The dress might look familiar as it's the same one the Duchess wore to the Windsor Horse Race last month (we all know she's a fan of re-wearing formal dresses).