When Linda McQuillen, a retired teacher from Madison, Wisconsin purchased her home in 1989 for $100,000, she had no idea she was getting a piece of 20th century architectural history, and she wouldn’t find out until 25 years later.

McQuillen had long imaged the 1,800-square-foot stucco home may have been designed by one of Wright’s peers or students in an imitation of his famed Prairie School style. But the first clue that it was perhaps something more than a copy came in 2009—20 years after McQuillen purchased the house just blocks away from the University of Wisconsin campus—when she received a letter from Wright scholar Mary Jane Hamilton.

Hamilton had long been engaged in research about Wright’s homes in his native Wisconsin, according to the AP, and had heard rumors about the house for years, but was never able to prove anything definitively. There were no references to it in any of the catalogs containing known Wright homes, nor were there any photos of the house after it was first built in 1917. The house also possesses some distinctly un-Wrightian elements, including a red brick lining on the wrap-around porch.

The breakthrough came when Hamilton found a 1917 Wisconsin State Journal advertisement by a Madison building company offering American System-Built Homes, Wright’s project to develop and market well-designed homes at a price affordable for the average American. The same company was listed on the 1917 building permit for McQuillen’s home.

Since having his “eureka moment,” as she calls it, Hamilton has worked to gather more proof, including finding a drawing among over 900 sketches in Wright’s Arizona archive that closely resembles McQuillen’s home. It has now been verified as an authentic Frank Lloyd Wright American System-Built House, one of 16 constructed, and one of just 14 still standing. It’s also the first and only known example of the AA model from the series that was actually built.

When McQuillen purchased the home in 1989, it was in such a state of disrepair that there was actually a tree growing through the roof. She told the AP that this news makes the hard work and money she’s invested in the structure well worth it.

“It does feel like a reward, a vindication that when I saw the house and could see beyond the disrepair that I knew there was something substantive. The house really spoke to me,” she said.

According to the Wisconsin State Journal, Hamilton and the nonprofit Frank Lloyd Wright Wisconsin are hoping to find people who may have known the 98-year-old house in its halcyon years, especially if they have photographs or information about it.