Prince William has kept his late mother, Princess Diana, close to his heart in the decades since her tragic death. "Remembering my mother, today and every day," William, 43, wrote via social media on Sunday, March 15. "Thinking of all those who are remembering someone they love today. Happy Mother's Day." Mother's Day is celebrated across the United Kingdom in March. For the Prince of Wales, he marked the occasion with a rare family photo. In the upload, Diana wore a pink sweater as she played with a toddler-aged William in a rose-filled field.