The book will "tell the truth" about their relationship, including his "sense of Sarah and my
perplexing fall from grace," The Telegraph quoted Johnston as saying. He also said, he''s doing it
"for me, for my boy Tripp and the country."
The Touchstone Publishing slates Johnston's book to be published in autumn.
It had earlier emerged that Johnston fathered a child with the former Alaska governor's daughter,
Bristol Palin, when they were teenagers.
The pregnancy was announced days after Sarah Palin was selected as the Republican vice
presidential candidate in 2008.
However, the couple broke up after the birth of their son, Tripp, reconciled shortly after, and are now
leading their separate lives. (ANI)