In the video below, Hagman and Josh Henderson take viewers behind the scenes of day one of production on the second episode, Hagman returns as J.R. Ewing and Henderson plays his son, John Ross.
Hagman recently revealed he's battling cancer, but his treatment may not interfere with his work on the series. He's expected to be in at least four episodes of the show.
"As J.R. I could get away with anything -- bribery, blackmail and adultery," Hagman said in a statement. "But I got caught by cancer. I do want everyone to know that it is a very common and treatable form of cancer. I will be receiving treatment while working on the new 'Dallas' series. I could not think of a better place to be than working on a show I love, with people I love. Besides, as we all know, you can't keep J.R. down!"
'Dallas' returns on TNT in summer 2012.