Bryan Cranston once served as Mark Harmon's understudy in a Los Angeles production of Wrestlers.

The Breaking Bad star, who is currently portraying former U.S. President Lyndon B. Johnson on Broadway, had to step in to take over for the NCIS star on three separate occasions.

However, during one show, Cranston found himself struggling to remember his lines.

He recalls, "It's a three-character play, mostly about these two brothers, and I was asked to understudy both of these characters and one of the actors was Mark Harmon and the other was the playwright...

"One time we were doing the play and I have all the dialogue raging in my head... and we're down there in front of the audience and Mark says his line and I just go blank. Couldn't think of the word at all, all eyes are on me. So I did a terrible thing to him and I said, 'Well you never know', and I know I looked at him like, 'Please help'. And he looked at me like, 'Oh, thanks a lot', because now the audience is all looking at him and going, 'He's not saying anything, he must have forgotten his lines'.

"Then, all of sudden, he threw out a line that got us back on track."