Prince William and Kate Middleton have revealed a heartwarming family tradition.

Every year, their children Prince George, 7, Princess Charlotte, 5, and Prince Louis, 2, make Mother’s Day cards for their late grandmother Princess Diana. The Princess of Wales, known as “Granny Diana” to his kids, died in 1997 at age 36, when William was 15. Photos of his children’s 2021 Mother’s Day cards for her were posted on Kensington Palace’s Instagram page on Sunday, March 14, aka Mothering Sunday in the United Kingdom.

George’s card was written on bright green paper. It read in cursive, “Dear Granny Diana, Happy Happy mothers day. I love you very much and think of you always, Sending lots of love from George xxxxx.”

Charlotte, whose full name is Charlotte Elizabeth Diana Mountbatten-Windsor, wrote her message to her late grandmother on light pink paper. She drew a heart with a rainbow design and surrounded it with small stickers of flowers, butterflies and a ballerina mouse.