Rod Stewart's memoir will be in stores on October 23.
Meanwhile, an excerpt to be published in Rolling Stone magazine on Friday, offers some bits about Elton.
The 67-year-old remembers the Christmas presents they exchanged, and even their nicknames for each other - 'Phyllis' and 'Sharon.'
"It was in the early 1970s that Elton and I drew especially close, the best of mates for a while," Stewart writes in Rod: The Autobiography.
Elton lived with his then-boyfriend just down the road from Rod in the countryside west of London, not far from one of the royal palaces at Windsor.
"Our mutual friend Long John Baldry had christened me 'Phyllis,' he had christened Elton 'Sharon,' and that's what we were to each other: Phyllis and Sharon. Or just 'dear'."
Stewart, who had scored by then with both the No. 1 single, Maggie May and No. 1 album on both sides of the Atlantic, also wrote admiringly of Elton's stamina for hard partying:
"I also had to be in awe of the fact that, whether it was drink or cocaine, he could see me right under the table every time."