David Harbour says the Red Guardian costume wasn't in the original 'Black Widow' script

• Harbour told Insider he originally was never meant to squeeze into the Red Guardian costume.
• "The first draft that I got the Red Guardian costume wasn't there," he said.
• The actor said the outfit was one of many things that evolved into the story.

One of the most memorable moments of the very first "Black Widow" trailer is when David Harbour's character, Alexei Shostakov, squeezes into his Red Guardian costume and comes out of the bathroom comically saying, "Still fits."

Turns out, originally we were never going to see Shostakov appear as the Soviet's answer to Captain America.

"The first draft that I got the Red Guardian costume wasn't there," Harbour revealed to Insider. "They put that bathroom scene in later."

Harbour said it was one of several elements that evolved as production began on the latest Marvel movie, which also stars Scarlett Johansson and Florence Pugh.

"We sat around and talked about the script," the "Stranger Things" star said. "The dinner scene in the trailers, a lot of that is us just messing around. Me grabbing food right in the middle of Scarlett's shot. They were developing the movie as we went. So there was a strong beginning, middle, and end but we were putting stuff in along the way."

"Black Widow," opening in theaters and on Disney+ on July 9, is the first standalone movie of Johansson's Avengers character Natasha Romanoff (aka, Black Widow). The movie takes place following the events of the 2016 Marvel movie "Captain America: Civil War."

On the run, Romanoff reconnects with her family from her youth, which was crafted by the Soviet government. Harbour's Shostakov character is her father figure. Rachel Weisz plays Melina Vostokoff, her mother figure. And Pugh is her sister figure, fellow spy Yelena Belova.

Harbour told Insider he would love to continue playing the Red Guardian character in the future.

His suggestion was perhaps a scenario where, instead of learning that she sacrificed herself in "Avengers: Endgame" to save humanity, he hears incorrectly about Romanoff's death and sets out to seek "vengeance."