Your family story has been a bit garbled, because your great grandfather doesn't seem to have been named after an actor, but rather after a character in a play. Perhaps your great-great-grandmother was fond of an actor who played the character.Claude
Melnotte is the hero of a play called The Lady of Lyons
by the English author Edward
Bulwer-Lytton. You can find information about the play here:http://www.encyclopedia.com/doc/1O149-LadyofLyonsThe.html
Melnotte does seem to be a real, if rare, French surname.