Prince Philip was taken from Norfolk to King Edward VII hospital in London on Friday morning, the BBC reports.
The 98-year-old Duke of Edinburgh was hospitalized for "observation and treatment" of a pre-existing condition, according to a statement from the palace. In the same statement, the palace said the trip was a "precautionary measure" and was taken "on the advice of His Royal Highness' Doctor."
The BBC adds that "it was a planned admission." He is expected to remain in the hospital for a few days.
Prince Philip has not been seen publicly since May, when he attended the wedding of Lady Gabriella Windsor. He retired from public life in 2017.
Earlier this year, the duke was involved in a car crash, and surrendered his license.
Prior to the hospitalization, the duke had been in Norfolk with Queen Elizabeth at their Sandringham Estate, where the couple celebrates Christmas every year. The Queen will soon be joined by Prince William, Kate Middleton, and their three children, Prince George, Princess Charlotte, and Prince Louis. This year, Prince Harry and Meghan Markle will not be attending the royal festivities. The couple, as well as their son Archie, are reportedly enjoying time away from royal life with Meghan's mom, Doria Ragland, in Southern California.