PRINCE William was involved in a rescue operation in rough seas and gale force winds after a cargo ship sank off the Llyn Peninsula.
One man is dead and five others are missing after the Swanland sank 30 miles out to sea in the early hours of Sunday.
RAF Valley 22 Squadron and Holyhead Coastguard spearheaded the rescue operation, which involved lifeboat crews from Pwllheli, Holyhead and Trearddur Bay.
Holyhead Coastguard watch manager Ray Carson said the 81 metre vessel was carrying 3,000 tonnes of limestone from Llanddulas to Cowes in the Isle of Wight.
“The second officer told us that the vessel was hit by, in his description, ‘an enormous wave’.
“She rolled and broke her back and from that point she lost her watertight integrity and sank rapidly,” he said.
The two rescued crewman, Roman Savin and Vitaliy Karpenko, suffered from shock but were otherwise unharmed.
They were taken to Ysbyty Gwynedd in Bangor.
Six helicopters were scrambled during the search, including RAF Valley 22 Squadron, with Prince William on board; RAF Chivenor and two from the Irish coastguard.
Holyhead Coastguard watch manager Barry Priddis said that the search for the crew of the sunken Swanland vessel was terminated at 5.30pm on Monday.
"We believe that from the time elapsed that there is no hope of finding anybody else alive," he said.
Ian Surthcott, UK Community Affairs Manager for Cemex who own the Raynes Quarry and Jetty said: "It's a tragic event and our thoughts are with the families of the men who were lost - and it has an impact on our workers here in North Wales."
He added that the Swanland was a regular visitor to the jetty.