Prince William admitted he was "feeling the nerves" on his first day as an air ambulance pilot.
The Duke of Cambridge completed a civilian pilot course in September last year, before undergoing specific 999-response training
He will cover Norfolk, Suffolk, Cambridgeshire and Bedfordshire in his new role.
Speaking after starting at 7am for his first shift, Prince William said he was "fantastically excited" and was looking forward to working with a "very professional bunch of guys and girls".
The royal also said he was enjoying being a father-of-two following the birth of Princess Charlotte, describing his daughter as a "little joy from heaven".
He described Prince George, who will turn two on July 22, as "a little monkey".
"At the same time there is a lot of responsibility especially when George is around - he's been a little monkey," he added.
There was little time to settle in as William and the rest of his crew were called out to their first emergency call at 9.20am.
More details about the incident are expected to be released later.
William said pressures from balancing the new role with his royal duties and family life would prove challenging, but said he was confident he could make it work.
"At some point there's going to be a lot more responsibility and pressure but at the moment I'm juggling it and enjoying it," he said.
William will work a nine-and-a-half-hour shift today as part of a four days on, four off rota system.
But he is expected to work about two-thirds of the shifts normally worked by pilots to take his royal duties into account.
William will be paid a salary for the role, all of which will be donated to charity.