Superstar Shah Rukh Khan was left amazed at Amitabh Bachchan's energy levels when he went for a special shoot on the 68- year-old megastar's quiz show "Kaun Banega Crorepati".

"KBC was fun though I am sure very tiring for Mr.B...hats off to him... (sic)" Shah Rukh posted on Twitter.

Shah Rukh, who is busy promoting his film "RA.One" these days, shot for the show in Mumbai Friday.

His superhero film is releasing this Diwali, Oct 26.