William, who is stationed with a Royal Air Force helicopter rescue operation in Anglesey, Wales, was in the crew of a Sea King scrambled into the search in the Irish Sea off Blackpool, the Daily Mirror reported.
Lifeboats were also involved in the search for the missing man. He was on the beach in Blackpool, a Lancashire coastal resort, when he was swept into the water shortly after midnight. A friend who was with him summoned help.
The searchers had to deal with rough seas and high winds. A second search was mounted after daybreak but also came up empty.
The coast guard said there is no hope the man could still be alive.
The prince was on his own in Wales for the New Year. He and his wife, Catherine, duchess of Cambridge, spent Christmas with her family at their home in Bucklebury, Berkshire, and then joined the royal family for part of the traditional celebration at Sandringham in Norfolk.
The duchess, who is pregnant, returned to Buckelbury.
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