The couple relocated to the U.S. soon after they announced their intention to step down from their roles as senior members of the royal family in January 2020.
Prince Harry, who is currently fifth in line to the throne, arrived in London on Friday, May 5, and is reportedly expected to return to California after the historic occasion at Westminster Abbey for his son's birthday celebrations.
He was last publicly seen with King Charles and his brother William - the first in line to the throne - in September 2022 at the funeral of his grandmother Queen Elizabeth II.
During Queen Elizabeth II's funeral, Prince Harry and Duchess Markle were relegated to the end of the second row beside Princess Beatrice and her husband, Edoardo Mapelli Mozzi.
Harry was, according to the Independent, reportedly not permitted to wear his military uniform to his grandmother's funeral despite serving 10 years in the army including two tours of Afghanistan.
He only wore it after being permitted by the King at the final vigil for the late Queen at Westminster Hall ahead of the funeral service, added the Telegraph.
On Coronation day, Prince Harry was also not permitted to wear the uniform and spotted a black three-piece set of tails and military medals on his chest as well as a Knight Commander of the Royal Victorian Order star around his neck.
The Prince was also relegated to the third row inside the abbey and was sandwiched between Princess Eugenie's husband Jack Brooksbank and Princess Alexandra.
Senior working royals; Prince William and Princess Catherine of Wales, the Duke and Duchess of Edinburgh - Edward and Sophie, sat in the front row during the historic ceremony, according to the Daily Mail.