Matthew Modine has long since hinted at his return as Dr. Martin Brenner a.k.a Papa in "Stranger Things" season 4, and recently leaked set photos from the set confirmed his appearance.

Fan account Stranger Things Spoilers tweeted a couple of photos of the actor behind the wheel of a car. He had a face mask on and a red bandanna on his head. The fan simply captioned the snaps, "he's back."

Modine played an important role in the first season of the Netflix series. He was missing in the succeeding seasons although his return was hinted in the third when a former Hawkins Lab employee told Eleven (Millie Bobby Brown) that her Papa is alive.

Fans initially thought Dr. Brenner died in season 1 after the monster attacked him at school. But the creators, The Duffer Brothers, have since said that if there was no dead body to begin with, then chances are the person or character is still alive.

Modine lived with this assurance as he hinted in previous interviews that his character is still alive. After all, no one saw the body. He teased that Dr. Martin Brenner is definitely going to be in "Stranger Things" season 4.

However, his return on what capacity, is still not known. Speculations have it that the scientist, and not Jim Hopper, is actually "The American" referred to by the Russian guards at the end of season 3. Perhaps he was taken prisoner since he knows more about The Upside Down and the monsters that live there. He may have a hand in the capture of the creature that the Russians have kept with them as teased by the season 3 end-credits scene.

Ding dong...

— Matthew Modine (@MatthewModine) September 30, 2019

Fans can probably expect more monsters in "Stranger Things" season 4 as Gaten Matarazzo, who returns as Dustin, teased that the instalment is the "scariest" yet.

"I think most would probably say it's the scariest [season] out of the previous three, which I love because it's very fun to film," he said in an interview with US Weekly.

"Stranger Things" Season 4 is still filming slowly but surely amid the pandemic. It is not yet known how many episodes Modine has. But his appearance on the set is clearly a big spoiler for Brenner's fate.

Matthew Modine
Matthew Modine speaking at the 2017 San Diego Comic Con International, for "Stranger Things", at the San Diego Convention Center in San Diego, California. Gage Skidmore from Peoria, AZ, United States of America / CC BY-SA ( Gage Skidmore/Wikimedia Commons