The book, titled "Kiss of Life", talks about the hardships he and his wife faced when their son was diagnosed with cancer at the age of four in 2014.
Shah Rukh, 51, and Emraan, 37, recently met and posed for pictures holding copies of the book.
SRK, sending his love for Ayaan, tweeted, "May Allah bless you & your family with health and happiness. Good to see u Emraan. My love to Ayaan."
Emraan said the meeting was a "fan moment" for him. "FAN moment :) !! Lots of love. Thank you for all your support @iamsrk," the "Hamari Adhuri Kahani" star tweeted.