Swedish Prince Carl Philip and his wife have gone into quarantine after testing positive for the coronavirus, the palace said on Thursday.
Both the prince, 41, and Princess Sofia, 35, have mild flu symptoms and were doing well under the circumstances, the statement added.
Carl Philip - fourth in line to the throne - married Sofia Hellqvist in 2015. They have two sons, who are also self-isolating.
The royal family's physician has begun efforts to trace the chain of infection.
King Carl XVI Gustaf, Queen Silvia, Crown Princess Victoria - Carl Philip's older sister - and Victoria's husband, Prince Daniel, were to be tested over the course of Thursday.
A funeral last Friday
Palace spokeswoman Margareta Thorgren told the daily Expressen that the royal family met last Friday for the funeral of German-born Queen Silvia's older brother, Walther Sommerlath.
Sommerlath died on October 23 at age 86. He had recently moved permanently to Sweden and lived at Drottningholm Palace, outside Stockholm.