Speaking with British GQ, the 36-year-old revealed how much he still misses her.
'I would like to have had her advice. I would love her to have met Catherine and to have seen the children grow up. It makes me sad that she won’t, that they will never know her,' he said.
Princess Diana passed away in 1997 after she was tragically killed in a car accident in Paris.
William says it's taken nearly two decades for him to speak openly about her death.
'I am in a better place about it than I have been for a long time, where I can talk about her more openly, talk about her more honestly, and I can remember her better, and publicly talk about her better,' he said.
'It has taken me almost 20 years to get to that stage. I still find it difficult now because at the time it was so raw. And also it is not like most people’s grief, because everyone else knows about it, everyone knows the story, everyone knows her.
'It is a different situation for most people who lose someone they love, it can be hidden away or they can choose if they want to share their story.'
The prince also touched on the importance of family.
'I could not do my job without the stability of the family,' he shares.
'I want George to grow up in a real, living environment, I don’t want him growing up behind palace walls, he has to be out there. The media make it harder but I will fight for them to have a normal life.'