David Harbour has opened up about his dramatic 34-kg weight loss for the fourth season of Stranger Things in a new Instagram post.

The actor, who plays police chief Jim Hopper on the hit Netflix series, appeared in season four looking visibly leaner to align with his character being imprisoned in a Soviet labour camp.

On Thursday (21 July), Harbour addressed fans who had asked about “Hopper’s physical transformation from season three to season four”, writing that he worked with his personal trainer David Higgins to lose “over 75lbs (34kgs)” for the role.

“All told it was a difficult and exciting ride, changing diet and exercise plans (or lack thereof),” Harbour, 47, captioned his carousel post which documented the physical transformation he underwent for Stranger Things.

The first photo was a split picture of Harbour on the show when he weighed “265-270lbs (120-122kgs)”, contrasted with when he was when he was “all the way down to 190lbs (86kgs) when we shot [season four]”.

“Second picture is me and David the week we began [training], my resistances and fury flaring,” his caption read.

In the third picture, a mirror selfie taken by Harbour after he dropped the weight and Stranger Things season four began filming, the actor’s body is marked with black Xs for “CGI scarring” in post-production.

Harbour also spoke about having to put on the weight again for a Christmas movie, in which he plays Santa Claus.

“Recently ballooned up again to play jolly ole St Nick in a flick I can’t wait for you to see this holiday season, so I am struggling to fight back down towards a good weight for wherever Hopper ends up in season five,” he told his followers, adding: “All this up and down is not good for the body, and I’ll have to give it up soon, but it is such a fun part of the job to live in a different version of your skin for a while.”

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Harbour promised to answer more fan questions about his dramatic season four transformation in an Instagram Live with Higgins on Friday (22 July) at 4PM BST.

During a recent interview, Harbour said he “doesn’t think” he’ll subject his body to such an intense regimen again, noting the “prosthetics are too good” now.