The two wore all black when they were spotted in the back of the car heading to St George's Chapel. The mother-of-three wore the Queen's pearls, a black face mask and a black fascinator with a lace veil during her outing.
The Japanese Pearl choker necklace has been worn by Kate before — she donned it at the Queen and Prince Philip's 70th wedding anniversary dinner in 2017, and Princess Diana wore it as well.
Earlier this week, Prince William, 38, paid tribute to his grandfather via social media.
"My grandfather’s century of life was defined by service – to his country and Commonwealth, to his wife and Queen, and to our family," the caption began. "I feel lucky to have not just had his example to guide me, but his enduring presence well into my own adult life – both through good times and the hardest days."
"I will always be grateful that my wife had so many years to get to know my grandfather and for the kindness he showed her," William continued.
"I will never take for granted the special memories my children will always have of their great-grandpa coming to collect them in his carriage and seeing for themselves his infectious sense of adventure as well as his mischievous sense of humour!" he added, referring to the snap of Philip with Prince George on a carriage.
"My grandfather was an extraordinary man and part of an extraordinary generation. Catherine and I will continue to do what he would have wanted and will support The Queen in the years ahead," he concluded. "I will miss my Grandpa, but I know he would want us to get on with the job."
William and Kate two of the 30 people who will attend Philip's funeral, which will begin at 3 p.m. U.K. time (10 a.m. EST).