The individual referred to as a "secret royal sister" in the context of Prince Harry and Prince William is Laura Lopes.
While not a direct blood relative, Laura Lopes is Prince William and Prince Harry's stepsister. This connection stems from Camilla Parker Bowles' marriage to King Charles III. Laura Lopes is Camilla's daughter from her previous marriage to Andrew Parker Bowles. This makes her a part of the extended royal family, although she maintains a relatively private life compared to other members. Her role within the royal sphere is primarily familial.
