Maria Puente and Ann Oldenburg, USA TODAY

Prince William fired the gun to start today's Anglesey ultra marathon.

But it was Duchess Kate who got things going with a bang as she delighted runners and fans with her surprise appearance.

This is the first time that new-mom Catherine has been seen at an official public event (she was snapped shopping for groceries earlier this week) since leaving hospital following George's birth on July 22.

Baby Georgie did not attend the event today.

William and Catherine sent runners off for the annual Ring O' Fire Anglesey Coastal Ultra Marathon, a 135-mile run that circumnavigates the Welsh island. It's part of their long goodbye to the place where they have lived for more than two years.

It had to be a little bittersweet for the couple, who will soon to leave Anglesey and move back to London with the little prince.

And Kate's appearance wasn't a total surprise. Palace officials had hinted she may appear with William at some public event in Wales before leaving for good, and three hours before the marathon started, press officials tweeted she would be there.

The two met volunteers and some of the runners and their families before the start of the event.

She was dressed in a olive-green tweed short jacket, a dot-patterned top, cropped black jeans and her favorite wedge shoes.He was just as casual in a blue sweater over a blue shirt.

The Daily Mail reported an insider said that initially she wasn't going to attend but "she was also keen for the chance to thank the people of Anglesey herself for the warmth and hospitality they have shown her and the Duke."

Kensington Palace announced this week that Will would officially start the marathon, leading to some initial confusion on Twitter about whether the 31-year-old second-in-line to the throne would be running in the race himself. He is not, even though he may want to.

Set against the dramatic backdrop of the Snowdonia Mountains, the marathon is staged over three days and follows the rugged and spectacular Anglesey Coastal Path around the island, home to the RAF base where Will has worked as a search-and-rescue helicopter pilot since before his marriage to the former Kate Middleton in 2011.

The couple and little George spent their first few weeks after the birth at her parents' estate in Bucklebury outside London, but they have been back in Wales for a couple of weeks. They're finishing up final duties and packing up their rented farmhouse to move into a huge new residence at Kensington Palace by October.

In between, they're expected to spend some time at Balmoral, the royal family's summer holiday estate in Scotland, visiting the baby's great-grandparents, Queen Elizabeth II and Prince Philip.

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