TORONTO -- Anderson Cooper has been immersed in some of the world's biggest news events, from wars to natural disasters and terrorist attacks.

But one of the most important experiences of his life has nothing to do with his lauded journalism career.

Rather, it was a late-in-life bonding experience with his mother, illustrious heiress/fashion designer/artist Gloria Vanderbilt.

It happened while making their revelatory new book, "The Rainbow Comes and Goes," and the HBO documentary "Nothing Left Unsaid."

Cooper said the book came about when his mom developed a respiratory infection and was seriously ill.

They started communicating via long email messages, and that correspondence makes up the book.

"I realize how much like my mother I really am and that's been really interesting," the CNN anchor said in a telephone interview.

"It's been life-changing for me to make that discovery, because then it allows me to look at the things she did and realize the mistakes she made and try to avoid those mistakes and things which I could very easily have done as well."

Both the doc and book detail the 92-year-old Vanderbilt's life, starting from her privileged upbringing and a custody battle waged by her young mother and her grandmother and aunt.

Dubbed the "poor little rich girl" by the press, Vanderbilt grew up under a glaring spotlight, hanging out with luminaries including Truman Capote and dating stars including Frank Sinatra.

She married four times and had four children, including Cooper and his brother Carter, who committed suicide in 1988. Another son, Chris, was estranged from her.

"We've always been close and I've always been sympathetic to her and viewed her as kind of a creature from a distant star that burned out long ago and who's sort of stranded here and been trying to figure out how to survive," said Cooper.

"But when you hear your parent's greatest regrets, and you see (how) the perspective my mom has on her life now is different than it was 10 years ago or 20 years ago, I understand her in ways I never did."

Writing back and forth was freeing and felt like having "a window into your past," he said.

"It was like putting a message in a bottle and just sending it off, only a response would come back in another bottle," added Cooper, 48.

"It definitely allows you to talk about things without the awkwardness sometimes. She brought up things which we had never discussed face to face and I don't know even that we would have."

In the book, Vanderbilt reveals that she believes her mother was a lesbian. She and Cooper also discuss the time he came out of the closet to her, and how her drinking was a problem when he was young.

They also discuss how both of their fathers died when they were young and how they both harboured a fantasy that their dads had left them a letter that would one day show up.

Cooper hopes the book will inspire others to start communicating with a loved one in a similar way and even make an audio or video recording of them so they can reflect on that footage.

"That's what I really hope people get out of it," he said.

"That it really does encourage people to talk ... (and) put aside past grievances and embarrassments and whatever the issues may be and to learn about the person before it's too late."