A girl aged 16 was rescued by Prince William after being swept out to sea trying to save her sister.
Rescuers said her sister, aged 13, had been swept away on a riptide while body-boarding and the girl had swam out to help her.
But she got into difficulties as she became exhausted and was close to drowning when she was winched to safety by an RAF rescue helicopter captained by Prince William.
The RAF said it was one of its 'fastest and shortest' operations, taking 38 seconds to arrive at the scene at Silver Bay, Anglesey, north Wales.
Flight Lieutenant Wales, 30, as Prince William is known in the RAF, piloted the Sea King while Master Aircrew Harry Harrison pulled the older sister, believed to be from Herefordshire, out of the water.
The incident happened close to the prince's RAF Valley airbase.
Vital time was saved because coastguards had called in the RAF immediately after being alerted to the emergency.
The younger girl had been saved by a surfer who took her ashore.
But the 16-year-old was battered by waves among rocks and vanished briefly under the surface when the Sea King arrived overhead.
Two surfers had been waving and pointing to the rocks to draw the attention of the chopper's crew to the exhausted youngster.
Onlookers had been unable to reach her as she struggled in the water.