Schumacher's signature was a shock - Paul Stewart

The Stewart family was astonished when they opened the bag to find Michael Schumacher's initials on Sir Jackie Stewart's legendary Formula 1 helmet.

During the Bahrain Grand Prix weekend, it was revealed that Schumacher, aided by his wife Corinna, had inscribed 'MS' on the helmet, joining signatures from all other living F1 world champions.

Bild newspaper reported that the helmet was shipped to the 56-year-old German's location via DHL.

"The (dementia) charity organisation was initially unsure whether it would be disrespectful to inquire with the Schumachers," the newspaper noted. "But the contact was made."

Corinna facilitated the effort, though Paul Stewart, who co-ran the Stewart F1 team with his father Jackie, admitted to doubts.

"Our family has known the Schumacher family for a long time," he said. "We weren't sure we would get the autograph until we saw it on the helmet. It was a wonderful thing—a once-in-a-lifetime experience."