Before he became a major movie star, Will Smith built up his acting resume through his television work—most notably as the star of The Fresh Prince Of Bel-Air. But his initial rise to fame came via his music career, where he made up one half of the Philadelphia-born hip hop duo DJ Jazzy Jeff & the Fresh Prince.

The pair found enormous success in the late 1980s, and embarked on their first major tour alongside legendary rap artists like Run-DMC and Public Enemy. There was just one difference between Smith and his tour-mates: DJ Jazzy Jeff & the Fresh Prince's songs (with titles like "Parents Just Don't Understand") were targeted at teens and decidedly PG-rated.

But why?

The answer lies with Smith's grandmother. In an interview on The Graham Norton Show in early 2015, Smith explained that "I started writing my raps when I was about 12. So I had my book—and, you know, I wanted to be a rapper! And I had all my curse words and my four-letter words and everything in there."

Then his grandmother found the book.

"She never said anything," Smith explained. "She just turned to the back page and she wrote 'Dear Willard... Truly intelligent people do not have to use words like this to express themselves. Please show the world that you're as smart as we think you are.'"

"From that point I never put profanity in my rap music," Smith said. And he (almost) never has.