Her dad’s mother
https://www.dailymail.co.uk/femail/article-13497751/prince-william-comments-kate-middleton-grandmother-love-attend-d-day-event.html
this is also an interesting story about a battle of egos
https://www.dailymail.co.uk/news/royals/article-13476631/Churchill-King-George-VI-D-Day-fell-out.html