ROME -- Pope Benedict XVI’s biographer revealed that the late pontiff for years suffered from insomnia and exhaustion, which ultimately led him to resign from the papacy.

The revelation, which was reported by the German magazine Focus, was confirmed by papal biographer Peter Seewald in a Jan. 27 interview with the German Catholic news agency KNA.

“Benedict XVI did not want to make a fuss during his lifetime about the intimate circumstances of his resignation, which was justified by his exhaustion,” Seewald told KNA.

According to Seewald, the late pontiff wrote a final letter to him Oct. 28, nine weeks before his death Dec. 31. In it, Pope Benedict told Seewald the “central motive” of his resignation was “the insomnia that has accompanied me uninterruptedly since World Youth Day in Cologne” in 2005.

Pope Benedict’s letter to Seewald adds further context to his shocking resignation in 2013. In his speech announcing his resignation, the late pope said that his health had “deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me.”

In his letter to Seewald, Pope Benedict said he was prescribed “strong remedies” by his personal physician at the time due to his insomnia. Nevertheless, the medication had “reached their limits.”

Knowing that he would no longer be able to “cope” with the rigours of travel for the World Youth Day 2013 in Rio de Janeiro, Seewald said Pope Benedict planned the announcement of his resignation so that a “new pope” would be able to travel.