David Harbour has shared new photos documenting the weight loss journey he went on between seasons 3 and 4 of “Stranger Things.”

Harbour, 47, posted the photos on Instagram on Thursday and revealed he lost 75 pounds between the two seasons of the hit Netflix show.

“Many of you have asked about Hopper’s physical transformation from season 3 to season 4,” Harbour captioned a series of photos. “My trainer @davidhigginslondon worked with me for 8months [sic] to make the transformation, and then another year to keep it through the pandemic.” Harbour described the process of “changing diet and exercise plans (or lack thereof)” as “a difficult and exciting ride.”

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The first photo in Harbour’s post is a collage showing his character, Hopper, shirtless in season 3 (top) and then in season 4 (bottom). The second photo shows Harbour with his trainer when they began training — “my resistances and fury flaring,” the actor wrote. The third and final photo is the day he shot one of his shirtless scenes for season 4. His torso is covered in black “x’s” which he says were added “for cgi scarring because of problems with the practical effect.”

“All told I lost over 75lbs. 265-270 in season 3 and all the way down to 190 when we shot,” Harbour said, noting however that he “recently ballooned up again to play jolly ole st. Nick in a flick I can’t wait for you to see this holiday season.” That film, “Violent Night”, will see Harbour play a murderous Santa Claus. But now that the project has wrapped he said he’s “struggling to fight back down towards a good weight for wherever [H]opper ends up in season 5.”

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Speaking about the dramatic changes his body has undergone, he commented, “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.”

David Harbour, Winona Ryder
From left: David Harbour, Winona Ryder, in Season 3 of “Stranger Things,” aired July 4, 2019. — Netflix / Courtesy Everett Collection/CPImages
David Harbour
A slimmed down David Harbour embodies the role of Hopper in “Stranger Things” season 4. — Netflix / Courtesy Everett Collection/CPImages

Harbour and his trainer, David Higgins, will be doing an Instagram live on Friday at 4 PM U.K. time. “Wanna answer questions you may have with @davidhigginslondon and tell you what I learned,” Harbour said.

Earlier this month, Harbour spoke about changing his body for roles in an interview with GQ Hype. “I don’t think I’ll ever do that again,” he told the fashion mag. “I have this Santa Claus movie coming out for Universal in December and I gained [it all back]. But now, yeah, never again. The prosthetics are too good.”