The 35-year-old Duke of Cambridge ends his job as a paid pilot for the East Anglian Air Ambulance (EAAA) after two years with a night shift from its base at Cambridge Airport.
Writing in the local 'Eastern Daily Press' newspaper, the second in line to UK's throne paid tribute to his colleagues.
"As I hang up my flight suit, I am proud to have served with such an incredible team of people, who save lives across the region every day," he wrote.
"I have watched as incredibly skilled doctors and paramedics have saved people's lives. These experiences have instilled in me a profound respect for the men and women who serve in our emergency services, which I hope to continue to champion even as I leave the profession," he wrote.
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"As a team, we travel to some very daunting incidents and we have been through some incredibly tough times together, witnessing some appalling tragedies," he writes.
"One of the first call outs I made was to a young man who had committed suicide; it was an incredibly tough day and had a profound effect on all of us, not least in my determination now to draw attention to this issue," he said.
William joined EAAA in March 2015 and after completing his final training flew his first operational missions in July 2015.
"As one would expect, there has been a lot of excitement surrounding William and his work with the charity. To us, he has simply been another hardworking member of the team; one of 11 highly respected pilots who help us to save hundreds of lives each year," said Patrick Peal, Chief Executive of the EAAA.
"We can't thank William enough for his hard work and commitment to the charity during this time. He has been a true professional, delivering our doctors and critical care paramedics to patients under testing conditions.
Pilot William Wales, as he is known at work, received a salary for his job which he donated in full back to the EAAA charity.
While on duty he worked as part of a close-knit team of four, on a nine-and-a-half hour shift, attending the worst medical emergencies of the 2,000-plus calls per day the service receives.
From September, he and wife Kate will move their children Prince George and Princess Charlotte primarily to their Kensington Palace home in London, as George starts school, and William and Kate commit all of their time to full time royal duties on behalf of grandmother Queen Elizabeth II and grandfather Prince Philip.
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