Prince William has told how "very traumatic" callouts involving children took him "over the edge" while he was working for the air ambulance.
The Duke of Cambridge served as a pilot at the East Anglian Air Ambulance until last summer, after moving from the RAF.
The prince, 36, said having his own children - George, Charlotte and Louis - deepened his feelings when sent to distressing jobs.
"I got very sad and very down about this particular family," he said.
Prince William worked alongside doctors and paramedics providing emergency medical cover across Bedfordshire, Cambridgeshire, Norfolk and Suffolk, as well as Essex and Hertfordshire at night.
"I worked several times on very traumatic jobs involving children," he said.
"After I had my own children, I think the relation between the job and the personal life was what really took me over the edge, and I started feeling things that I have never felt before.
"Talking was really important, but even that wasn't quite enough for one particular incident for me."
Prince William, based at Cambridge Airport for two years, praised both the East Anglian Air Ambulance and the RAF for their good mental health practices.
He has previously shared how his experiences of piloting had "some very sad and dark moments".
The duke spoke at the first This Can Happen conference in London, which aims to tackle mental health issues in the workplace.
He urged employers to look after the mental health of workers and said he felt responsible for looking after his own staff, who can work "silly hours".
"There should be a much more open, supportive and compassionate working environment," said Prince William.
"There's still a stigma about mental health. We are chipping away at it but that wall needs to be smashed down."
He campaigns alongside the Duchess of Cambridge and the Duke of Sussex for mental health initiative Heads Together.