Prince William was joined by his wife Kate Middleton in paying tribute to his late grandmother, Queen Elizabeth — on a day that also sees his brother Prince Harry’s return to the U.K.

On Monday, Sept. 8, the third anniversary of the monarch’s death, the Prince of Wales, 43, visited the Women’s Institute in Sunningdale, Berkshire, near his Windsor home and was also accompanied by the Princess of Wales in a surprise move. The outing was especially poignant: Queen Elizabeth, who died in 2022 at Balmoral Castle in Scotland, was an enthusiastic member of the WI for 80 years and served as its president from 2003 until her death.

Kate, 43, who wore a black checkered dress for the outing, wasn’t initially expected at the engagement.

During the visit, William and Kate met members from Berkshire and beyond to hear how the organization — the U.K.’s largest women’s group — fosters connection, skills and community projects. He also listened as members shared stories of Queen Elizabeth’s time with the WI, where she would join in over tea, cake and lively conversation.

The outing comes just hours before Prince Harry, 40, is set to appear in London for the WellChild Awards, a cause close to his heart. He arrived earlier in the day for the event and other engagements this week.

A source tells PEOPLE that the prince is in a “positive” mood upon his arrival in the U.K. on Monday.

“He’s in a really good headspace and looking forward to seeing everyone from his charities and the causes he cares about,” the source says.

Earlier on Monday, the Duke of Sussex also paid his own special tribute to his late grandmother as he visited the burial place of Queen Elizabeth at St. George’s Chapel in Windsor to pay his respects privately and lay a wreath of flowers, a spokesperson for the duke confirmed to PEOPLE.

Meanwhile, King Charles and Queen Camilla are spending Accession Day privately at Balmoral, PEOPLE understands. The King and Queen also attended Crathie Kirk, a church near the Balmoral estate, where prayers were said to mark Accession Day and for Katharine, the Duchess of Kent, who died on Sept. 4 at the age of 92.

The brothers’ overlapping schedules highlight the continued strain in their relationship, as they are not expected to meet during Harry’s visit. Kensington Palace confirmed that William will carry out royal duties Monday through Wednesday, directly coinciding with Harry’s planned public appearances. While the brothers aren’t expected to cross paths, speculation continues over whether Harry will reunite with his father, King Charles.

The Women’s Institute was a beloved part of Queen Elizabeth’s life. In 2017, members told PEOPLE how excited they were to see her join a WI meeting following an illness. “After her severe cold, it was lovely to see her. She looked so pretty in that [megenta] color,” Mary Relph said.

Members also recalled a presentation on author Jane Austen by historian Lucy Worsley. Yvonne Browne, vice president of the West Newton WI, added, “We put on the Sandringham WI version of Cinderella. She seemed to enjoy it. She was very relaxed and chatted. We had a lovely afternoon.”

The year before, members marked the Queen’s 90th birthday a little early, raising a toast with Champagne and sharing a slice of fruit cake during her visit.

In a statement after her death, William reflected on his grandmother’s role in his life: “She was by my side at my happiest moments. And she was by my side during the saddest days of my life. I knew this day would come, but it will be some time before the reality of life without Grannie will truly feel real.”

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He also reflected on the support Queen Elizabeth had given his wife Kate and their children — Prince George, 12, Princess Charlotte, 10, and Prince Louis, 7. “While I will grieve her loss, I also feel incredibly grateful,” William said. “I have had the benefit of The Queen’s wisdom and reassurance into my fifth decade. My wife has had twenty years of her guidance and support. My three children have got to spend holidays with her and create memories that will last their whole lives.”

William and Kate’s joint outing fell days after they attended separate matches as part of the Women’s Rugby World Cup on Saturday, Sept. 6. While Kate attended the match between England and Australia, William was was seen at the game between Wales and Fiji in different locations in England.

At the match and during her visit to the WI, Princess Kate’s blonde hair transformation appeared to be a thing of the past. The royal’s hair seemed to be back to her signature brown, after she was seen with blonde hair earlier in the week, with her tresses styled in loose curls on Monday.