The 80-year-old's bushy brows have prompted much online discussion from fans - even inspiring a spoof Twitter account - with Dallas head of make-up Lynn Barber telling Entertainment Weekly that Hagman refuses to have them trimmed.
"First thing Larry said when I met him was, 'We don't cut my eyebrows. We just maintain them and we groom them'. And I said, 'Yes, sir'.
"They're stronger and better than ever. Most times as people age, we lose the eyebrows. They get thinner. Larry's have almost gone the opposite way. I can't imagine Larry without those eyebrows."
Barber insisted that Hagman's thick eyebrows add to the "alpha male" persona of his Dallas character J R Ewing.
"Can you imagine if those brows were manscaped? No," she laughed. "No. It wouldn't be right."
She added that the brows "have a life of their own" and increase Hagman's time in make-up before shooting.
"In the morning, after doing his make-up, I would just wet my fingers with a little water, sometimes put a product on there if one [of the brows] was giving me problems, and we'd just swoop 'em into that form that they had, like horns."
Dallas continues on Wednesdays at 9/8c on TNT. The show will premiere in the UK on Channel 5 later this year.
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Watch a trailer for the new Dallas below: