Casually dressed in a striped jumper, black leggings and flat Sebago shoes, with her hair pulled back into a ponytail, the 31-year-old pushed her trolley around the aisles picking up supplies for herself, Prince William and their baby boy.
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Her reappearance on the Welsh island was certainly unexpected — it was widely assumed that Kate and Prince George were still holed up at the Middleton family home in Bucklebury, Berkshire.
But it seems mother and son have travelled more than 250 miles to join Prince William, who returned to work as an RAF search and rescue helicopter pilot two weeks ago.
Both William and Kate hold great affection for Anglesey, which has been their first home together as husband and wife. It is thought that they will say goodbye to the island next month, and move into their recently renovated home in Kensington Palace.
William and Kate with baby George, pictured at the Middleton family home by Michael Middleton
During an appearance at the Anglesey show recently, new dad William took to opportunity to thank local residents for their hospitality.
"I know that both of us will miss it terribly when my search and rescue tour of duty comes to an end next month and we have to move elsewhere," the Duke said.
"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.
"This island had been our first home together, and it will always be an immensely special place for us both."
The Duchess spent the first weeks of maternity leave at the Middleton family home in Bucklebury
William has been stationed as a pilot at RAF Valley at Anglesey since 2009. It is largely thought that he will return to London to join his regiment, the Household Cavalry's Blues and Royals, and care for his new family there.
William and Kate have been afforded a sense of normality during their time on the island, where they have been living in a rented farmhouse. It's little surprise then that Kate wanted to spend time there as she gently prepares to return to life in the spotlight as a royal mum.
On 12 September, the Duchess will attend her first official royal engagement since the birth of her son on 22 July.
The new parents will be guests of honour at the inaugural Task Conservation Awards, it has been reported.
Last week, they shared the first official photo of Prince George. The touching and informal family snapshots, taken by Kate's dad Michael Middleton, show the Duke and Duchess proudly posing with their tiny son, who is a "little bit of a rascal" according to William.
During his first interview as a father, William joked, "He either reminds me of my brother or me when I was younger. I'm not sure, but he's doing very well at the moment."