Unlike in previous years, the Sussexes and the Cambridges did not participate in the Queen's processional, meaning they went directly to their seats without any fanfare.
Meghan, 38, wowed in a kelly green Emilia Wickstead cape dress with a matching William Chambers fascinator hat and beige Aquazzura heels. Harry, 35, donned a navy suit, but when the wind whipped up, the green lining of his jacket revealed he was secretly matching his bride.
Kate, 38, and William, 37, arrived shortly after the Duke and Duchess of Sussex, with Kate in a dark red coat dress and matching hat that she paired with a sleek up 'do. William wore a dark suit and a tie that matched his wife's look.
All eyes are on the reunion of the Fab Four -- their first public meeting since Harry and Meghan announced their decision to step down as senior members of the royal family. Though they didn't have a big reunion moment, Harry and Meghan were seated directly behind Kate, William, Queen Elizabeth II, Prince Charles, and Camilla.
At one point, William and Kate were spotted talking with Prince Edward and his wife, Sophie, who were seated next to Harry and Meghan, but the two brothers and their wives were not seen interacting.
Meghan, Harry, Kate and William were last spotted together in November at Remembrance Day events, though they were not photographed interacting at the time.
"The brothers don’t hate each other as has been reported," a royal source told ET, adding that "they do talk."
The annual Commonwealth Day service is held at Westminster Abbey in London. The Sussexes and Cambridges both attended last year and were photographed together.
Harry and Meghan are currently visiting the United Kingdom ahead of their official March 31 transition where they will step down from being senior members of the royal family. After the decision was announced in January, the couple went to Vancouver Island, Canada, with their 9-month-old son, Archie.
Harry returned to the U.K. in late February and was later joined by Meghan for some final royal events before the transition. The couple previously attended the Endeavour Fund Awards last Thursday and the Mountbatten Music Festival over the weekend.
For more on Meghan and Harry, watch the clip below: