Bert Convy acting in Nanny and the Professor.
This got me interested, so I checked Bert's IMDb page. Turns out this guy had quite an acting career, with 73 credits from 1951, when he was just eighteen, to 1990, the year before his death. It's unlikely that anyone would confuse Convy's acting ability with Olivier's, but the guy was good enough to keep getting work in a bunch of TV shows.
One of his odder credits was on One Step Beyond, an ABC anthology show that ran from 1959 to 1961 and offered a lot of goofy, way-out subjects. It was more or less the alphabet net's (Variety speak) version of Twilight Zone. YouTube has preserved Bert's episode for your viewing pleasure. He plays Professor Andersson, a poor sap who's lost in the desert with a couple of annoying companions. Strange things happen, but none of them involve a game show.
Bert appeared in no less than seven eps of Love Boat, and his acting career generally veered toward that kind of light entertainment. It's a little hard to imagine him playing Hamlet, after all.