Jeff Bezos pens Amazon review for Lauren Sánchez's book: How many stars did he rate it?

Jeff Bezos may have started Amazon and now serves as its executive chairman, but he doesn't leave many reviews of the company's products.

Unless his fiancé Lauren Sánchez is involved.

Sánchez's new children's book “The Fly Who Flew to Space” (32 pp, The Collective Book Studio) was released earlier this month and is already on the USA TODAY Best-selling booklist and The New York Times children's picture books best seller list.

On Amazon, it has a rating of 4.9 out of 5 stars, including one that is very short and specific.

"This is the best children’s book my fiancée has ever written," Bezos wrote Sept. 18. Sources confirmed it was a verified purchase from Bezos, who clicked five stars and titled the review "Six stars." We thought he'd get an advance copy.

Check out: USA TODAY's weekly Best-selling Booklist

Bezos has only ever written nine Amazon product reviews, with the last left in 2006 about milk when he rated it 5 stars and wrote, "I love milk so much that I've been drinking it since the day I was born. I don't think it was Tuscan though." He has also left reviews for a book about the solar system, cookies, cheese snacks and binoculars.

Lauren Sánchez's book urges kids to dream big

The charming and playful book has a message every parent hopes their children receive: Anything is possible. Stay curious. Dream Big. It is published in Spanish and English.

Her kids inspired herLauren Sánchez reveals how her children helped her write her new book

The book follows Flynn, a fly who struggles in school, but finds her passion in space. Sánchez, a pilot, says the idea came from a fly that was trapped in the cockpit of a plane she was flying with her kids.

When she wrote the book, she decided the fly should go higher than an airplane and go to space. She, of course, was more recently inspired by Bezos, who owns private space exploration company Blue Origin. He even appears as a fly on page 2.

"Being around someone who is just so dedicated to pushing the boundaries in exploring the unknown is incredibly inspiring to all of us in the family," she says. "Our dinner conversations often revolve around space and innovation. He really just challenges us all to dream big. At the dinner table I was saying something and he said, 'No, dream bigger. Go bigger.' So it's not a surprise that some of that excitement found its way to Flynn's adventure."

Sánchez has sent the past weeks promoting the book with events at bookstores for children, as well as celebrity endorsements from actresses such as Jessica Alba and Eva Longoria.