The cast of the 1970s sitcom "Three's Company" was, from left, Joyce DeWitt, John Ritter and Suzanne Sommers. Ritter died in 2003.

It's been more than 40 years since "Three's Company" debuted on ABC, quickly becoming one of the most-watched sitcoms of the 20th century. Now 70 years old, Joyce DeWitt was new to the Hollywood ...