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Anderson Cooper opened up to Megyn Kelly tonight about a riveting new documentary and book on his family story.

Cooper and his mother, Gloria Vanderbilt, recently co-authored a new book called “The Rainbow Comes and Goes,” and they are featured in the HBO documentary “Nothing Left Unsaid.”

In a broad-ranging interview on The Kelly File tonight, the CNN anchor explained that the inspiration of the book stemmed from the aftermath of losing his father at age 10.

“I always had this fantasy growing up that he had written me a letter, and maybe that letter would show up, when I turned 18, or when I turned 21, and it would tell me all about his life and what he wanted from my life,” he said.

“Of course, there wasn’t any letter.”

Cooper later found out that his mom “had the exact same fantasy about her father,” whom she lost at 15 months old.

“I realized, when my mom turned 91, I didn’t want to have that fantasy about my mom when she’s no longer here,” he said.

“So we started this project together of emailing each other, and just me asking her questions, her asking me questions, and getting to know each other in a new way.”

Cooper also discussed the tragedy his mother later went through, with the deaths of her husband and her son.

“My brother committed suicide in front of her when he was 23 and I was 21. But you know, she has this incredible resilience, and I think that’s one of the things that really comes out in the book and the film is that she has this drive and determination to survive.”

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