The Duke of Cambridge, second in line to the British throne, will finish his brief career as an air ambulance pilot in the east of England with a night shift.
The move comes as his grandmother Queen Elizabeth II and her husband, the Duke of Edinburgh, take a step back from royal duties and leave the younger generation to take their place.
Reflecting on his time flying medical crews from a base at Cambridge Airport, William praised the dedication of those who work for the emergency services.
"As part of the team, I have been invited into people's homes to share moments of extreme emotion, from relief that we have given someone a fighting chance, to profound grief," he wrote in an editorial published by The Eastern Daily Press.
Residential gardens, school fields and beaches have all been used as makeshift landing pads as the air ambulance crew rushed to the most serious medical emergencies.
"As a team, we travel to some very daunting incidents and we have been through some incredibly tough times together, witnessing some appalling tragedies," William said.
William, elder son of British heir Prince Charles, detailed some moments which had stuck with him, such as the "incredibly tough day" when he was called out to a man who had committed suicide.
William said the experience had made him all the more determined to draw attention to mental health, a cause he has championed alongside his wife Kate and brother Prince Harry.
Before his final shift, William was described as "not only a fantastic pilot, but a much loved and valued member of the crew" by Patrick Peal, chief executive of the East Anglian Air Ambulance.
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