To mark Mother’s Day in the UK on Sunday, Kensington Palace shared sweet cards that Kate Middleton’s children—Prince George, Princess Charlotte and Prince Louis—made for their Granny Diana. In her card, Princess Charlotte, five, revealed how she sweetly refers to her dad, Prince William, as “papa.”

©Kensington Palace

“Dear Granny Diana,” the little Princess began. “I am thinking of you on Mother’s Day. I love you very much. Papa is missing you. Lots of love Charlotte.”

George, seven, also penned a heartfelt message for his late paternal grandmother. “Dear Granny Diana, Happy Happy Mother’s Day. I love you very much and think of you always. Sending lots of love from George,” the future King wrote.

Kensington Palace revealed that every year on Mother’s Day, the Cambridge kids make cards remembering their grandmother, who passed away in 1997, for Prince William. The Duke of Cambridge has spoken in the past about keeping his mother Princess Diana’s memory alive for his kids by “constantly talking about Granny Diana.”

“We’ve got more photos up around the house now of her and we talk about her a bit,” he shared in the 2017 Diana, Our Mother: Her Life and Legacy documentary. “It’s hard, because obviously Catherine didn’t know her so she cannot really provide that level of detail, so I do, regularly putting George and Charlotte to bed, talk about her and just try and remind them that there are two grandmothers, there were two grandmothers, in their lives and so it’s important that they know who she was and that she existed.”