Maria, who never married and never had any children, eventually became a secretary and housekeeper for Joseph Ratzinger as he was promoted to cardinal. She died of a heart attack in 1991 at the age of 69.
Long before he was named pope himself, Jospeh Ratzinger had the ear of Pope John Paul II, and served as his close advisor. Hesemann said Pope John Paul II often sought Ratzaginer's advice and the two would have collaborated on how best to offer the famous grand apologies Pope John Paul II made for the wrongdoings of the Catholic Church.
"In every step John Paul II made, you have one way or the other, an influence of the Ratzinger theology," Hesemann said. "John Paul II was a wonderful communicator but, as they say, he was not a great theological professor, he was not a teacher of theology, he was not a theological genius, and so he needed Ratzinger."
However, having his brother named pope "shocked" Georg Ratzinger at first, not because he was jealous, Hesemann said, but because Georg knew it meant he would not be able to retire and travel with his brother as they both had planned.
"It was a shock for him, it was a shock. He was deeply depressed," Hesemann said. "He did not go to the phone for one day. His brother the pope tried to call him many times and in the end, eventually the housekeeper went to the phone, and picked it up, and there's pope on the other line. He wanted to talk to his brother, and so for him, he said, 'Oh my God, I don't want to talk to anybody, this is the worst thing that could happen because now it's like I don't have a brother anymore, he won't have any time for me.'"
Even now, Hesemann said Georg won't call his brother because he doesn't want to disturb him, but Georg will travel to Rome four times a year to spend time with the pope.
"He's happy to have him be the pope," Hesemann said. "[But] he is missing his brother. He would like to have his brother at his side."
Georg Ratzinger's recollection of his family in the book seems overwhelmingly positive, and Hesemann said it's because the Ratzingers were a tight-knit family who prayed together -- Ratzinger even broke down in tears when talking about the deaths of his parents and his sister, Maria.
Hesemann said he and Georg Ratzinger wrote the book, in part, as a reply to what Hesemann called the "crisis of the church" and the "crisis of family," meaning there are more divorces than ever now and priestly vocations are low.
"In America you have a beautiful saying, 'a family that prays together, stays together,'" Hesemann said. "The Ratzinger family secret was they prayed together... when they had a problem in the family the problem was solved in prayer and that's why it became such a harmonic family."