 Along with Colin Gordon, McKern was one of only two actors to play Number Two more than once.He first played the character in the episodes "The Chimes of Big Ben" and "Once Upon a Time", and later reprised the role in the final episode, "Fall Out".The filming of "Once Upon a Time" proved to be a particularly intense experience for McKern; according to one biographer, the stress caused him to suffer either a nervous breakdown or a heart attack (accounts differ), forcing production to stop for a time.