ABC/Randy HolmesElton John surprised some old classmates when he made an appearance at a reunion of his senior school, Pinner County Grammar School, over the weekend. According to Hello! magazine, the 68-year-old pop-rock legend attended the northwest London school until he was 17, when he left to pursue a career in music.

Hello! says Sir Elton flew to the U.K. from Las Vegas to take part in the event. He posted a couple of photos from the reunion event on his Instagram feed. One pic shows the singer and 14 other people smiling, and includes a caption from John that reads, “Lunch at home with dear old school friends. Many of whom I haven’t seen for 50 years! It was as if we never left school. So much laughter and so many wonderful memories.”

Another photo captures Elton with a man named Keith Francis, whom he calls his “oldest pal…A wonderful, loyal friend for 57 years and still counting!” John reveals that Francis “flew all the way from Australia for our class reunion.”

John kicks off a European tour May 31 in Kent, U.K.

Meanwhile, today marks the 40th anniversary of the release of Captain Fantastic & the Brown Dirt Cowboy, John’s ninth studio effort. The album was the first ever to debut at #1 on the Billboard 200 and remained at the top of the chart for five weeks. The album also yielded the #1 hit “Someone Saved My Life Tonight,” and has gone on to sell more than three million copies in the U.S. alone.

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Lunch at home with dear old school friends. Many of whom I haven’t seen for 50 years! It was as if we never left school. So much laughter and so many wonderful memories. #ShareTheLove #PinnerCountyGrammarSchool #Classof58

A photo posted by Elton John (@eltonjohn) on May 17, 2015 at 1:35pm PDT

My oldest pal Keith Francis. A wonderful, loyal friend for 57 years and still counting! He flew all the way from Australia for our class reunion. Love you so much. #ShareTheLove #PinnerCountyGrammarSchool #Classof58

A photo posted by Elton John (@eltonjohn) on May 17, 2015 at 1:40pm PDT