The Duchess of Cambridge has made her first public appearance since the birth of her son George today (August 30).

She surprised organisers by agreeing to attend the start of an ultra-marathon in Anglesey with her husband Prince William.

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Paul Lewis/The Daily Mail

The Duchess joined the Duke at the beginning of the 135-mile Ring O'Fire race on the island, where he has been based during his time as an RAF search and rescue pilot.

The royal couple met some of the event's participants and volunteers, before starting the race.

Their son Prince George of Cambridge, now 5 weeks old, did not attend the event.

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Paul Lewis/The Daily Mail

The Duchess's first official post-baby appearance was originally due to be at the inaugural Tusk Conservation Awards on September 12.

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The couple welcomed their first child on July 22, with Prince George weighing in at 8lb 6oz.

Prince George of Cambridge meets the world's media - photo gallery:Royal baby boy leaves hospital