Transcript for Prince Harry opens up about needing therapy after the death of his mother, Princess Diana

Finally tonight here, nearly 20 years after losing his mother, tonight the new interview with prince Harry on his mother, his struggle and how he wants to free others from their pain, too. It was nearly 20 years ago, prince Harry was just 12, saying good-bye to his mother. This week, prince William, prince Harry and duchess Kate teaming up for what's called heads together. Harry opening up about the therapy he needed after losing his mother. Prince Harry saying just tonight in a new interview, he heard from so many others who have suffered. After years of listening to stories from veterans and their families and then hearing some of the most heartwrenching stories based around what people have experienced it was only -- it was only right to share my experiences and to help, to hope, encourage others to come forward. Reporter: And so he did. With extraordinary candor this past week. I can safely say that losing my mum at the age of 12 and therefore shutting down all of my emotions for the last 20 years has had a quite serious effect on not only my personal life, but also my work as well. Reporter: Describing the depths of his sadness after losing his mother. I've probably been very close to a complete breakdown on numerous occasions. Reporter: His campaign with his brother to end stigma around mental health. Need to remove the stig that around mental health. Reporter: What would his mother think. I think she would be proud of the campaign and proud of us. She would be overwhelmed and hugely encouraged by the fact that the uk not knowing for wanting to talk about mental health issues has suddenly gotten to this point. Helping to remove the stigma. I hope to see you right back here tomorrow. From all of us here at ABC news, good night.

This transcript has been automatically generated and may not be 100% accurate.