We should all be grateful that two of the happiest people in the world found each other and formed a beautiful friendship. The Dalai Lama and retired South African archbishop and freedom fighter Desmond Tutu have written a book together to share some of that joy. The Book of Joy outlines eight pillars of joy, according to principles of the mind and heart.

Written with co-author Douglas Abrams, The Book of Joy chronicles a discussion between the two friends after Tutu, 85, flew to Dharamsala to see his old friend last year and mark the Dalai Lama’s 80th birthday. A few years earlier, the Dalai Lama was prevented from attending Tutu’s 80th birthday party after South African officials bowed to pressure from China.

“I was very sad to miss your birthday,” the Dalai Lama says to Tutu, in an extract published on Buddhist website Lion’s Roar. In an online video to promote the book, the two friends often hold hands or poke each other in playful displays of affection.

“He’s always teasing me,” Tutu laughs in the extract published on Lion’s Roar, recalling how His Holiness likes to steal his hat. In the published extract, the Dalai Lama talks about how much he misses the ailing Tutu when the he and the other Nobel Peace Prize laureates meet.

“But when you are not there, something [is] missing, really,” said the Dalai Lama.

“Thank you. I paid him,” the Archbishop responds.

“I don’t know that you wake up in the morning and say I’m going to become a friend to the Dalai Lama. It just happens. Scientists will come afterwards and analyze it,” Tutu said, according to the extract published online. “When we kept quiet, our hearts discovered that they were kindred spirits.”

The “spiritual brothers”—as they call each other—believe that people are innately good, with a deep desire to find “lasting happiness in a changing world,” according to the book’s subtitle. The Dalai Lama and Tutu know just how violently one’s world can change. Tutu spent decades outside South Africa fighting apartheid and is still considered the country’s moral compass. The Dalai Lama remains exiled from Tibet, but leads the call for compassion and peace in the world.

“I think I would be very sulky, and I think there’d be a part of me that was always sad and it would show in my face. It doesn’t in his,” Tutu says in the extract of his friend’s exile.

Thank you,” the Dalai Lama said.

“Pay me, pay me,” says Tutu.

“I will pay. I will pay with a few nice words.”

Published by Penguin Random House on Sept. 20, The Book of Joy is already a New York Times bestseller.