Kate Middleton and Prince William reveal the cute Mother's Day cards their children made for Princess Diana

• The Duke and Duchess of Cambridge's children write a yearly Mother's Day card for Princess Diana.
• The royal couple published cards made by Prince George, Princess Charlotte, and Prince Louis on Twitter.
• The Cambridge kids refer to their late grandmother as "Granny Diana."

The Duke and Duchess of Cambridge have revealed that their children write an annual Mother's Day card for their late grandmother Princess Diana.

Prince Wiliam and Kate Middleton shared this year's cards on the Kensington Royal Twitter account on Sunday - the British date for the celebration honoring mothers.

"Each year on Mother's Day, George, Charlotte, and Louis make cards remembering their Granny, Diana, for William," the royals wrote. "Whatever your circumstances, we are thinking of you this Mother's Day."

-The Duke and Duchess of Cambridge (@KensingtonRoyal) March 14, 2021

"Happy, happy mother's day," 7-year-old Prince George wrote in his card. "I love you very much and think of you always."

Princess Charlotte also made a card for Princess Diana. "Dear Granny Diana," wrote the 5-year-old royal. "I am thinking of you on Mother's Day. I love you very much. Papa is missing you."

The youngest child, two-year-old Prince Louis, painted a heart and added stickers to his card.

Prince William talks about "Granny Diana" when putting his children to bed, Insider's Talia Lakritz previously reported.

He has continuously made an effort to keep her memory alive since the royal's death in 1997, Lakritz said.

The Duke and Duchess of Cambridge dedicated a hymn to Princess Diana at their wedding and honored her by making one of Princess Charlotte's middle names 'Diana.'