Princess Beatrice ran alongside 5,000 members of the public who were chosen to inaugurate the new Olympic Stadium in East London on Sunday.
Beatrice had been given the number 2012 in honour of the games and was in charge of firing up competitors.
After ringing the klaxon, she joined the crowds and crossed the finish line in a respectable 45 minutes 45 seconds.
It's not the first time that Beatrice has put on her running shoes.
In 2010 she became the first royal to complete the London Marathon.
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