The royal family's staff said the duke, known as Prince Philip, was hospitalized in Aberdeen as a "precautionary measure," The Daily Telegraph reported. He was said to have felt ill Wednesday morning.
Philip, 91, announced when he turned 90 he was cutting back on his public schedule. But he still appears at many events with and without his wife.
He spent six days in a London hospital in June after developing a bladder infection during the official Diamond Jubilee weekend. Last Christmas, Philip was taken to a Cambridge hospital where he was treated for a blocked artery.
The royal couple attended the opening ceremony of the London Olympics July 27, and Philip, admiral of the Royal Yacht Squadron, was in Weymouth Aug. 1 for sailing events. He watched his granddaughter, Zara Phillips, compete in equestrian eventing, winning a silver medal.
This week, Philip was on the Isle of Wight for two days at events involving the yacht squadron.
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