In the final stretch of making its iconic 1975 album “Toys in the Attic,” Aerosmith stumbled upon inspiration for “Walk This Way” while strolling through the seedy streets of Hell’s Kitchen and Times Square.

“‘Walk This Way’ was the last song that we had to finish,” “Toys in the Attic” producer Jack Douglas exclusively told The Post. “But we could not come up with a lyric or a melody line or anything.”

Taking a break from the studio sessions at the Record Plant in Midtown Manhattan, they went searching for a stroke of creativity in the city.

“Because of the pimps and hookers and drug dealers, there was always a lot of good material on the street,” said Douglas.

But on this particular Sunday afternoon, “it was barren,” he said. “There was nobody on the street.”

So they gave up and turned to the movies.

“I suggested that we take a break and go see ‘Young Frankenstein,’” recalled Douglas of the 1974 Mel Brooks flick starring Gene Wilder. “And there’s a scene where the hunchback [played by Marty Feldman] says, ‘Walk this way,’ and they all walked this way, which totally broke us up. That was so hilarious.”

And when they got back to the studio, Steven Tyler said, “I got it! He went into the stairwell, and about an hour or two later, he came back with the whole trip.”

Co-written by Tyler and guitarist Joe Perry, “Walk This Way” would go on to become the biggest hit off of “Toys in the Attic,” Aerosmith’s third LP that was released 50 years ago on April 8, 1975. Also featuring such classic rock staples as “Sweet Emotion,” the title track and the power piano ballad “You See Me Crying,” it went nine-times platinum, becoming the best-selling album of the group’s legendary career.

“You know, the drugs worked,” said Douglas with a laugh. “We were still at that point where we weren’t crazy yet, but we could spend those extra hours on stuff.”

Indeed, “Toys” established Aerosmith as a band to be taken seriously.

“People made fun of, ‘They’re trying to be the Rolling Stones. They’re trying to be this or trying to be that,’” said Douglas. “But that album proved that they were more than all of the things that people thought of them. They proved to be the really great American rock band that they wanted to be.”

Having flown up to first meet Aerosmith at the band’s Boston home base — “They were playing in a high school,” he said — the producer had previously produced Aerosmith’s 1974 second album “Get Your Wings.” But they were ready to take flight to the next level — and then some — on “Toys in the Attic.”

“They went out on the road for a year, playing those [‘Get Your Wings’] songs … and when they came off the road, they were an entirely different band,” said Douglas. “They had improved 100% or more. So it was a whole new thing.”

With the band not having much time to write on the road, Aerosmith and Douglas spent a few months in preproduction shaping the material for “Toys in the Attic” before heading into the studio at the Record Plant.

“We didn’t want every song to sound the same,” said Douglas, noting the influence of The Beatles. “We were big Beatles fans, and the thing about The Beatles with the late albums, every track was different. They all had a different elements to them.

“And so as we went through the songs, I would set up the studio different. I would tune the drums differently, I would make sure that the keys were different, so that each song had its own character.”

The full spectrum of Aerosmith was on sweet display on “Toys in the Attic.”

“Their influences came through, shined through,” said Douglas. “Their R&B influence, their blues influences, came out during that record.”

“Sweet Emotion” — written by Tyler and bassist Tom Hamilton — started with the latter’s lick for the ages.

“He started just playing that bass line to jam along with,” said Douglas. “And when [drummer] Joey Kramer started playing to it, he came in on the wrong side. He came in backward. And Steven and I went, ‘Oh my God, that’s genius!’ He’s playing on the other side of the beat, which makes that bass line more prominent.

“And Jay Messina, who was my engineer, played bass marimba. And so he doubled that bass line with the bass marimba,” he added.

As for the rowdy, guitar-riffing title track that opens the album, Douglas said, “We wanted to start the album with a barn burner, just kick it off with something that just grabs your attention right away.”

“Joe Perry brought that lick in, and we developed it,” he explained. “We knew right away it was going to be a super hard-rocker, super up-tempo. And off we go.”

“Toys in the Attic” paved the path for other American bands to rock their own way.

“I think that it created a template for many bands that followed,” said Douglas, noting its influence on everyone from Guns N’ Roses to Nirvana.

And “Walk This Way” would also have a big impact on hip-hop when Run-DMC covered it in 1986 in collaboration with Aerosmith. In fact, both versions are in the Grammy Hall of Fame.

“I liked it,” said Douglas of Run-DMC’s groundbreaking overhaul produced by Rick Rubin.

“I was in the south of France in a restaurant, and a waiter brought over a bottle of very expensive champagne … and said it was compliments from that gentleman over there. And I looked over, and it was Rick Rubin. And he went, ‘Thank you.’”

Douglas went on to work with Aerosmith on 1976’s “Rocks,” 1977’s “Draw the Line” and 1982’s “Rock in a Hard Place.” Still, “Toys in the Attic” remains the album that forever bonded him to the band that was enshrined into the Rock & Roll Hall of Fame in 2001.

“We were really focused on making that record,” he said. “It made us all the brothers that we still are.”