Prince William has opened up about his mother's death in a documentary on mental health, calling it "pain like no other pain".
The British royal also reveals his experiences as an air ambulance pilot left him acutely aware of the presence of death.
Dealing every day with families "having the worst news they could possibly have" left him with a "very depressing, very negative feeling", he explained.
William (36) said Princess Diana's death in 1997 in a Paris car crash meant he could relate to others who had suffered a bereavement.
"I think when you are bereaved at a very young age, any time really, but particularly at a young age, I can resonate closely to that, you feel pain like no other pain," he said.
"And you know that in your life it's going to be very difficult to come across something that's going to be even worse pain than that.
"But it also brings you so close to all those other people who have been bereaved."
Speaking in BBC documentary A Royal Team Talk, William said the characteristic "British stiff upper lip thing" had its place, but people also needed "to relax a little bit and be able to talk about our emotions because we're not robots".
He also revealed that before his air ambulance experiences became a "real problem", he sought help.
In the programme, the prince teams up with footballers Peter Crouch, Thierry Henry, Danny Rose, Jermaine Jenas and England manager Gareth Southgate for a talk about mental fitness.
He speaks candidly of how he found the emotional side of being an air ambulance pilot "very difficult".
"It leaves you with a very depressing, very negative feeling, where you think death is just around the door everywhere I go. And that's quite a burden," he said.
"That raw emotion… I could feel it brewing up inside me and I could feel it was going to take its toll and be a real problem. I had to speak about it."
William and brother Harry have talked extensively about how they dealt with their mother's death as they promoted their Heads Together mental health campaign.
A Royal Team Talk: Tackling Mental Health will be screened on BBC One tomorrow at 10.30pm.