The Princess of Wales congratulated Arthur Fery on his run to the semi-finals and wished him a happy birthday.
William's squad included former England captain Mark Tomlinson and Saudi businessman Amr Zedan.
The princess completed the challenge in aid of the hospital where she was treated for cancer.
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After greeting queuing fans and handing out tickets to attendees, the princess took a seat on court 18.
Ted and his father say it was incredible bumping into Catherine, Princess of Wales.
The surprise encounter with the Princess of Wales happened at the top of Ben Nevis.
The Princess of Wales did the endurance event to raise awareness about "holistic healthcare" for cancer patients.
The Princess of Wales and the couple's children share message for "the best papa in the world".
