The air ambulance returned to its Cambridge base at 1.30am, at the end of William’s final shift.Meanwhile, Prince William was also spotted in a park in Royston, Hertfordshire, on his penultimate job.He was seen sitting in the helicopter at around 7.05pm after attending an emergency call out to an elderly woman who had suffered leg injuries following a fall. The woman was then taken by air ambulance to Addenbrooke’s Hospital in Cambridge, where she remains in a “life-threatening condition”, the East of England Ambulance Service said.A mile-long stretch of the B1135 Wymondham Road in Hethel, home of Lotus Cars, remained closed on Friday as the Independent Police Complaints Commission (IPCC) investigated.The rural road has farmers’ fields on either side. The woman was struck at around 10.20pm on Thursday and nobody else was injured. A Norfolk Police spokesman said: “In accordance with normal procedure, Norfolk Police has referred the matter to the Independent Police Complaints Commission.”An air ambulance spokesman said: “The EAAA crew, which last night included William, attended an incident south of Norwich which involved a road traffic collision-related injury, and a patient was treated at scene for severe head injuries then treated at Addenbrooke’s Hospital.” Prince William starts his final shift with the East Anglian Air AmbulanceCredit:Heathcliff O’Malley He joined EAAA as a pilot in March 2015 and, after completing an initial period of job- specific training involving simulator, aircraft and in-flight skills, he began piloting his first operational missions in July 2015.Throughout his service, William has been based at Cambridge Airport, as part of a team including specialist doctors, critical care paramedics and pilots providing emergency medical services across Bedfordshire, Cambridgeshire, Norfolk and Suffolk. The helicopter left around 7.35pm without picking anyone up as the casualty was taken by land ambulance to Addenbrooke’s Hospital in Cambridge.Tracy Stressing, who lives near the park, said: “I had just heard the news on the radio that it was Prince William’s last day and then a friend called to say he had just landed in the park nearby. I couldn’t believe it and rushed there to take some photos.”The Duke announced in January that he would be ending his career with EAAA and has clocked up more than two years flying medical crews to emergencies. Prince William’s career The Duke of Cambridge flew a critically-injured pedestrian to hospital on his final shift as an air ambulance pilot.The woman, in her 50s, had been reported missing when she was struck by a marked police van in Hethel, about eight miles south-west of Norwich.Officers were responding to a 999 call “relating to concerns for the safety” of the woman, Norfolk Police said.Prince William’s East Anglian Air Ambulance (EAAA) crew was called to the scene at 11.13pm on Thursday and the critical care team treated her at the scene for complex serious head injuries. A statement issued by Kensington Palace earlier this year said William and Kate wanted, as they had in previous years, to increase their official duties on behalf of the Queen and their charity work, which would mean more time in London. The Duke of Cambridge starts his final shiftCredit: Heathcliff O’Malley Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.