Britain's Prince William co-piloted a helicopter which rescued two people early on Sunday, after a ship was hit by an "enormous wave" in the Irish Sea, the UK's Press Association reported.
One person died and another five are still missing after the 81-meter cargo carrier sank some 10 miles west of the Llyn peninsula in north Wales, the news agency said.
William, who also has the title The Duke of Cambridge, was called into action from his base at RAF Valley after the Swanland ship issued a mayday call at around 2am (0200GMT) when its hull cracked.
Two members of the Russian crew of the Cook Islands-registered vessel were pulled from the water soon after the alarm was raised. They were airlifted to safety by William's Sea King helicopter and were later taken to hospital in Bangor for precautionary checks, the Press Association said.
The Royal Air Force (RAF) later released dramatic video footage of the rescue, said to have been filmed from the helicopter William was co-piloting. At one point, the winchman attempting to reach two survivors in a life raft is seen to land in the water some meters from the raft. In a later attempt, he manages to grab on to the raft and effect the rescue.
Another crew member was found in the water later in the morning but has been confirmed as dead, said the Maritime and Coastguard Agency.
A spokesman for the Ministry of Defence said: "The Duke of Cambridge was a co-pilot on one of the aircraft involved. He is now back at base."
Gale-force winds battered the Irish Sea during the early hours of the morning and the Coastguard believe this could have been what caused the incident.
The 81-meter cargo carrier was carrying 3,000 tons of limestone from Colwyn Bay to Cowes in the Isle of Wight.