The 53-year-old politician, not known for being particularly personable in public, told the newspaper Bild on Wednesday his hair turned grey quickly in 1980 due to a health problem – something only his wife has known until now.
According to the paper, Steinmeier was diagnosed with a corneal ulcer that threatened vision in both eyes shortly before he was scheduled to take his exams to become a lawyer in his early 20s.
Steinmeier's doctors decided to perform a cornea transplant from an organ donor – a procedure that was uncommon at the time, Bild reported.
“Many anxious days and hours followed until the operation was successful, his eyesight saved,” the paper wrote.
But the blond student's hair turned grey almost immediately.
“Until then he had a few grey hairs at most,” a former fellow student told the paper.
But Steinmeier, who faces popular Christian Democratic (CDU) Chancellor Angela Merkel in the upcoming election, joked with the paper about the dramatic change.
“I have to dye it every day so the black roots don't grow out,” he told Bild.
But all kidding aside, he said the surgery compelled him to make a personal decision to always carry an organ donor card.