Just off Mecox Bay on the beautiful shores of Hayground Cove sit four breathtaking waterfront acres. For decades the cozy home on this property belonged to actor Cliff Robertson, an Oscar winner for 1968’s Charly who portrayed everyone from President John F. Kennedy and Buzz Aldrin to Uncle Ben in 2002’s Spider-Man in his storied career. Sadly, this Hollywood legend and longtime Hamptons resident passed away before he could complete his vision for his Water Mill estate. But, for the first time, a new owner has an opportunity to see Robertson’s plans come to fruition.

It isn’t only pedigree that makes 36 Morrison Lane so special. Unlike anything else on the East End, this four-acre lot is actually two properties in one. “What’s unique is that it’s two contiguous building lots that are each two acres,” explains Harald Grant, Senior Vice President at Sotheby’s International Realty. “Most properties only have one certificate of occupancy, but because this is actually two separate lots that are joined, it allows you to have a main house and a guesthouse, both with accessory structures.”

What does that mean for the buyer of this $19.5 million estate? Well, the property already boasts Robertson’s home, a six-room, 4,000-square-foot gambrel-style residence with living rooms on the ground and upper levels, plus outdoor space that includes magnificent gardens and landscaping, a swimming pool, a tennis court, and access to a dock on Hayground Cove. But sitting between that cozy cottage and the water you’ll find two pristine acres that are primed for building.

Set on more than 265 feet of direct waterfront with its own separate dock, the property’s second lot is ready for new construction that would turn 36 Morrison Lane into a world-class estate unlike any other in the Hamptons. “The front lot has roughly a 20,000-square-foot building envelope,” Grant explains, “meaning you can build a nice house with a pool and tennis court.”

The jaw-dropping vistas across Hayground Cove would only be accentuated by a new residence. “The first floor would be at a 12 to 14 foot level, giving you great views of Mecox Bay and sunsets,” says Grant as he envisions the home that could fit in this oversized lot. And it only gets better. “The second floor, which would probably be at 20 feet, will have views of the bay as well as the ocean.”

When seen in this context, Robertson’s move-in ready home becomes what the actor always intended: a two-bedroom guesthouse behind a waterfront main house. “A lot of people in this price category have friends who are extended family, and now they can be accommodated,” says Grant. “You can have guests living in a separate house on your same property.” And though the house is in pristine condition, there is another option: remove it to build a second main residence with a massive building envelope of 28,000 square feet.

Whether the buyer of 36 Morrison Lane chooses to keep it as is or create an unparalleled East End compound, they will get to enjoy the wonders of Water Mill, an intimate hamlet with under 2,000 residents. “There are some nice, isolated properties like this one in this area off of Mecox,” says Grant. “It’s tucked away, but you’re not far from the shopping and restaurants in the center of other villages.”

That solitude is a real selling point. Mary Cummings, archivist at the nearby Southampton Historical Museum, points to location as the reason why Water Mill transformed from a humble place to harvest oysters centuries ago to, in just the past few decades, one of the country’s most exclusive zip codes. “It’s very beautiful and has a lot to offer, but one of the main reasons is that it is also very small,” Cummings explains. “There are only so many places around the water in Water Mill.”

To be on the water is one thing, but the chance to turn this blank canvas into the estate that Cliff Robertson always envisioned is the real treasure. “I knew Cliff,” remembers Grant. “He himself was going to build a great house there. That was the whole plan.” By doing so, the buyer of 36 Morrison Lane will continue the legacy of this beloved actor, pilot, horseman and, most importantly, local institution. “He really enjoyed the Hamptons,” says Grant. “He was a real Hamptonite.” Harald Grant, Sotheby’s International Realty, 50 Nugent St., Southampton, 283-0600