EXCLUSIVE: 85-year-old Disney cartoon “Harem Scarem” unearthed by D23 and studio archives (VIDEO)

Before Mickey Mouse made his seminal appearance in "Steamboat Willie," there was Oswald the Lucky Rabbit in "Harem Scarem."

As part of Disney's D23 fan celebration event, the Disney fan club and the Walt Disney archives has compiled the oldest known cartoon from the company's eponymous creator and has shared the video exclusively with Yahoo News.

"This is a prime example of the kind of thing that we're digging out of the vaults, going the extra mile to show the fans something new and unique," Disney archives director Becky Cline told Yahoo News.

"There's no new Walt Disney history to share unless we dig it out and discover it."

Oswald the Lucky Rabbit: The original Mickey Mouse

Walt Disney worked as an animator for Universal for several years before launching his own Disney empire. And one of the major successes he helped create for Universal was the character Oswald the Lucky Rabbit.

In total, 26 Oswald the Lucky Rabbit cartoons were produced for Universal in the 1920s and '30s with Disney and Ub Iwerks, who was Walt Disney's long-time collaborator. In fact, it was Universal's first-ever cartoon series. Though Oswald has his own unique characteristics, it's clear to any observant fan that he provided much of the basis for what would become Mickey Mouse, arguably the most iconic animated figure in history.

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However, things began to sour between Disney and producer Charles Mintz when the Winkler Productions head wanted to lower production costs and cash in on the character's popularity.

"Walt was so creative and always trying to push the envelope. Not to compensate himself but to make the character better and to make the animation better," Cline said.

"Walt didn't understand that the contract he had signed gave Mintz ownership of the character. He was absolutely devastated. He wanted to do things his way."

After getting out of his contract with Universal, Disney embarked on a long, lonely train ride back home to California.

"On the way back on the train back to Hollywood, Walt was sending telegrams to his brother and came up with the idea of Mickey Mouse," Cline said. "He had a mouse he used to feed on his art board back in Kansas City. Mickey was kind of born in secret."

"It was a hard break for Walt. He truly was devastated," Cline said. "Walt was only 27-years-old when he lost the character."

Bringing Oswald Home, the "Al Michaels Trade"

For more than six decades, the Disney company would continue to flourish, but Walt Disney never lived to see Oswald come back into the fold. But in 2006, Disney CEO Bob Iger would change Disney history in one dramatic move.

Disney was in the middle of negotiating the contract of sportscaster Al Michaels, who was interested in returning to NBC Sports. The negotiations were reportedly amicable on both sides, but Iger seized the opportunity to turn a peaceful parting into an unusual swap.

"Nobody ever thought it would happen," Cline said. "Bob popped up in the middle of negotiations and said, "We want Oswald back." By 2006, most people had completely forgotten about Oswald the Lucky Rabbit.

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Cline says information and bios on Oswald were gathering dust while hidden away in "deep storage" in Disney's archives. So Universal readily agreed to the trade and Oswald came home.

"Walt would be so excited about having Oswald back," Cline said. "And for a Disney fan, to get the character back in the fold, is really exciting. To see something they've never seen before."

Disney threw a homecoming party for Oswald on the day he was "signed" and has slowly been integrating him back into the overall branding strategy.

He appeared in the Disney video game Epic Mickey and is rumored to be a leading character in the game's sequel after Disney promoted the character at this year's E3 gaming conference.

2012 is the 85th anniversary of the character. To celebrate the milestone, Disney wanted to do something special. That's when Cline and her team of archivists came across some of Walt Disney's original Oswald sketches. Not wanting to alter the original works, they embarked on a painstaking process to place the sketches in order, as is, to create a basic animating effect.

During a private D23 "Disney Fanniversary" event for fans in Burbank, San Francisco, New York and Boston, Disney unveiled the animation, titled, "Harem Scarem." And now it is being shown to the public for the first time.

"We wanted to do something unique and cool. We went into our animation files and discovered that we had a lot more art than we thought we did," Cline said.

"We scanned the original artwork. Scanned every single page, put them together in order. In the end, we created a piece, about 90 seconds of animation. You can see that the animation is adorable. No bells and whistles."

Disney is scheduling more D23 fan events for the rest of the year during which they will show off the Oswald content along with several other properties having anniversaries, including cartoon series "Duck Tales" and characters Goofy and Daisy Duck.

And on July 6, the "Treasures of the Walt Disney Archives" will open at the Ronald Reagan Library in Simi Valley, Calif., featuring more previously unseen Disney content, including Oswald drawings and artwork.

"Oswald is going to have even more fans after this," Cline said. "It's not a big stretch to see Mickey coming from Oswald. Oswald's a bit of an anarchist and a lothario."