(CNN) -- Robert Lamoureux is sitting on a $1.8 million waterfront home in Rhode Island -- but he shouldn't get too comfortable.
The developer awaits a judge's ruling on when the palatial three-story home must come down, after an appeals court ruled that it was built on already-owned park land, court documents said.
The Narragansett property was built in 2011 by Lamoureux's company, Four Twenty Corp., on land owned by The Rose Nulman Park Foundation, according to a Rhode Island Supreme Court opinion.
"I hoped to work it out from Day One when I found out," Lamoureux told CNN. "But it couldn't be achieved, and I can only say that I'm disappointed and I have to move on."
Lamoureux originally acquired the land in 1984 and divided it into two lots -- one of which later turned out to be on land already owned by the foundation, according to the opinion.
In 2009, Lamoureux hired an engineering firm to survey the land and obtain a building permit. Because of a surveying error, it was not immediately apparent that one lot was already owned by the foundation.
Four Twenty Corp. entered into a sale agreement, but the prospective buyers later conducted another land survey and discovered that the home was located on the Nulman property, according to the opinion.
The Rose Nulman Foundation was set up to preserve the waterfront land as a park in perpetuity, allowing free public access, according to the foundation's lawyer, Mark Freel.
Upon learning of the survey, Lamoureux told CNN on Tuesday, he contacted the foundation to determine if an agreement to purchase the land could be reached but was told that the structure would have to be taken down or moved.
The prospective buyers backed out of the sale as a result, according to the opinion.
Freel told CNN that the decision to remove the home was the right one.
"We always thought it was the right outcome. We are very pleased," Freel said, adding that the foundation has always intended to use the land as a public waterfront park.
The court ruling called the matter an "unfortunate situation" and said that, while Lamoureux has "clean hands," any outcome other than the removal of the home would be "unjust."
Paul Ryan, legal counsel for Save the Bay -- a environmental group whose goal is to protect and restore the Narragansett Bay -- told CNN affiliate WJAR that there have been many instances where errors resulted in waterfront homes being built over property lines.
A Rhode Island trial judge will determine when the home must be taken down by, according to the opinion.