Sir Ian McKellen joins the Cookie Monster on Sesame Street

Having trod the boards in Shakespeare and captivated viewers in The Lord of the Rings, Sir Ian McKellen has scored perhaps his most bizarre part yet – teaching the Cookie Monster about temptation in Sesame Street.

The clip released yesterday shows the actor, 75, teaching the blue-haired creature about the meaning of the word “resist”.

“The word resists means to control yourself and stop yourself from doing something you really want to do," Sir Ian explains.

As the Cookie Monster struggles to understand the concept, the actor plays on his role as Gandalf in The Hobbit and The Lord of the Rings and draws a golden ring from his pocket.

“Say there was a golden ring and you really really wanted and this golden ring was like your precious. You want this ring so badly that if you were able to control yourself and not go near the ring you would resist it," he says in the clip.

When the Cookie Monster still doesn't grasp the idea, Sir Ian confronts him with a giant chocolate chip cookie. Needless to say, the Monster doesn't last long and snatches the cookie from Sir Ian's hands and devours it.

Sir Ian is the latest in a long line of famous faces to appear on the children’s TV show, including Benedict Cumberbatch, Robert de Niro, Jessica Alba, and Cameron Diaz.