Prince William is honoring his late mother Princess Diana. On Sunday, the 43-year-old took to Instagram to share a heartfelt and never-before-seen photo of the people's princess, AKA his momma. In celebration of the UK's Mother's Day, which is on March 15, the Prince posted the vintage pic, which sees him as a child with Princess Diana in a beautiful meadow. He wrote on the official Prince and Princess of Wales account: "Remembering my mother, today and every day. Thinking of all those who are remembering someone they love today. Happy Mother's Day.