Prince Harry spent years after his mother's death believing she would return to "whisk" him away.

The Duke of Sussex was just 12 years old when Princess Diana passed away in a car crash back in 1997 and it took him a long time to process the fact she was gone for good.

In a new MasterClass titled Redefining Grief: Building Resilience Through Loss, Harry told neuroscientist Dr. Mary-Frances O'Connor: "I believed that she had created this exit to get away from all the things that were destroying her life and that she was gonna reenter the fray in some disguise and then whisk me and my brother away."

Mary insisted Harry's belief wasn't "crazy".

She said: "When we bond with someone, when we fall in love with our spouse, or you fall in love with your baby, that's actually encoded in the brain as a 'we' that says, 'I will always be here for you, and you will always be here for me.'

"And so when a loved one dies, that is not evidence for the brain to give up that they are everlasting. We still believe that they are out there, that they are just lost, that we need to find them, that we yearn for them because we still expect that they're gonna walk through the door.

"You're not crazy. It's an important part of your brain that holds attachment-bonded relationships together by believing they're out there."

Harry - who has Prince Archie, now seven, and daughter Princess Lilibet, five, with wife Meghan, Duchess of Sussex - struggled to find happiness because he felt "guilty" about doing so without Diana in his life but eventually experienced a "huge mental shift" that completely changed his outlook on life.

He said: "I'd spent so long emotionally numb, to a large extent, because I felt disloyal and guilty for the possibility of being happy and joyful without her.

"I felt like I had to be sad and I had to be emotionally numb in order to prove to her that I missed her.

"But the reality is, what I discovered was actually that she just wanted me to be happy. And that was a huge mental shift for me. It freed me, and it gave me a whole different outlook on life."

The 42-year-old prince is driven by a desire to make his mother "proud" and his charity work has given him an outlet to carry her legacy on.

He said: "Everything I do, everything I put my energy towards, I hope that my mother will be proud about it.

"Trying to continue and protect her legacy, what I didn't realise was the work that I ended up choosing, or the work that I ended up getting drawn in and attracted to, was so similar to the work that she was doing.

"With grief comes this, it's not so much responsibility, but this carrying of the person that you've lost throughout your life.

"There is an element of carrying my mother in me that ultimately energises me for the work that I do."