Tuxedo — The doughnut hole in Sterling Forest has just been closed.

Sterling Forest LLC, owners of the last major piece of private, undeveloped land in the nearly 20,000-acre state park, sold that 571-acre tract this afternoon to New York for $13.5 million, a major victory for environmentalists who fought plans to develop the property.

Lou Heimbach, the company president, said afterward he was pleased with the outcome. His company had proposed to build 103 luxury homes and a golf course on the site — later modified after the presence of timber rattlesnakes scuttled the golf course.

"I think it was a very win-win situation for all parties," he said.

The plans to develop that pocket of land within a vast stretch of parkland had long inflamed the environmentalists who labored to preserve Sterling Forest from a much grander development scheme.

The big building plans fell by the wayside when the state bought most of Sterling Forest. But what remained after several land sales was that 571-acre tract off Route 84, referred to by activists as a "doughnut hole" they still hoped to preserve.

Their fight against Heimbach's Sterling Forge project gained traction three years ago when consultants discovered timber rattlesnakes — a threatened species in New York — on the site.

To avoid encroaching on the rattler's protected habitat, Sterling Forest LLC was forced first to trim the number of planned homes and then jettison the 18-hole golf course. The company reconfigured the design to include slightly more houses.

Nonetheless, opponents continued speaking out against the project, which they saw as a threat to the surrounding nature.

Heimbach, who has long maintained he would sell for the right price, said this afternoon that he and the state agreed on that amount in May or June and then met yesterday at his attorney's office in New Windsor to conclude the deal.