The Duchess of Cambridge joined husband Prince William at the Ring O' Fire Anglesey Coastal Ultra Marathon on Friday afternoon (30 August).
In footage aired on BBC News, Kate, 31, looked radiant as she watched William launch the marathon on the island that the couple called home for many years.
The Duchess' appearance was kept secret until today; it had been thought she'd make her first post-birth appearance at the Tusk Trust charity ball on 12 September.
Kate gave birth to her first child, George Alexander Louis, at St. Mary's Hospital in Paddington, London on 22 July. He wasn't with his parents today.
We saw the royal the day after the birth when she posed with William and their newborn outside the Lido Wing, and again the following day when the new parents were snapped taking little George to Kate's parents' home in Bucklebury, Berkshire.
This month, the couple released the first pictures of George since the hospital photocall, choosing to use intimate family pictures taken by Kate's dad Michael Middleton rather than a professional photographer.
While Kate has kept a low profile, William has been seen out and about, most recently at the Angelsey Show on 14 August, where he told onlookers that Kate and George would have loved to attend.
In his speech, William had joked: "[George] is pretty loud and, of course, extremely good looking. I thought search and rescue duties over Snowdonia were physically and mentally demanding but looking after a three-week-old baby is right up there."
William and Kate have been living at a cottage in Anglesey since 2009 while Wills worked in the area as a search and rescue pilot. He will leave next month, with the family expected to take up residence at Kensington Palace.
"From the bottom of my heart, thank you for making my wife and me so welcome when we arrived here, as you do thousands of visitors each year," he said.
"This island had been our first home together, and will always be an immensely special place for us both. Catherine and I look forward to returning again and again over the coming years with our family."
William gave his first in-depth interview since George's birth earlier this month, saying the youngster is a "little rascal" and probably takes after himself and brother Prince Harry.
"I think the last few weeks for me have been just a very different emotional experience. Something I never thought I would feel myself," he said in the chat, which airs on CNN on 15 September.
"And I find, again it's only been a short period, but a lot of things affect me differently now."
Prince George's first photocall in pictures: