The Duke of Cambridge stunned Madison Lambe when she visited the Sandringham Estate by seizing her mobile phone and taking a pic of himself and the schoolgirl.
Now Madison is the most envied pupil at her school after posting the image of herself standing with the future king on Facebook.
She said: "I couldn't believe it when William came over to me and I asked for a picture. He just said to me 'you can't beat a good Selfie on Christmas Day' and took the picture.
"It was really good, I didn't expect it. He was really nice and I was so excited. I've put the picture on Facebook. My friends think it is really good and they have been commenting on it."
Madison had travelled with her mum Paula Scrupps, 38, from their home in Boston, Lincolnshire, to Sandringham to watch the Royals walk to church.