Prince William has called the death of his mother, Princess Diana, "a pain like no other"

Speaking in new BBC documentary, 'A Royal Team Talk: Tackling Mental Health', William, 36, said: "I think when you are bereaved at a very young age, anytime really, but particularly at a young age - I can resonate closely to that - you feel a pain like no other pain.

"And you know that in your life it's going to be very difficult to come across something that is going to be an even worse pain than that.

"It also brings you so close to all those other people out there who have been bereaved. So instantly, when you talk to someone else… You can almost see it in their eyes sometimes."

William also spoke about how his previous work as an air ambulance pilot, which saw him confronted by loss on a daily basis, left him with a "very depressing, very negative feeling".

He explained: "You're dealing with families who are having the worst news they could ever possibly have – on a day-to-day basis.

"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 to carry and feel.

Speaking of the "particular, personal' resonance he felt with some families, he added: "That raw emotion, I just thought listen, I can't – I could feel it brewing up inside me and I could feel it was going to take its toll and be a real problem.

"Even though you don't necessarily know the individual or the family, you share someone's pain – because we all do. We all have families, we can all relate to it.

"I had to speak about it... when you see somebody at death's door, with their family all around them, it's a very hard thing to describe."