Real estate heiress, architect and socialite Serena Rhinelander Stewart has listed her Upper East Side co-op at 115 E. 67th St. for $3.95 million.

But the unit was formerly owned by the late author Kathleen Winsor, who penned a novel, “Forever Amber,” detailing the sexcapades of a heroine in 17th-century England.

The book was banned in 14 US states as pornography because of its sex scenes and abortion references that were scandalous at the time.

The novel became a bestseller in the 1940s and was even made into a 1947 film produced by 20th Century Fox.

Rhinelander Stewart bought the three-bedroom, three-bathroom pad in 2004 — the year after Winsor’s death at age 83.

It comes with a library that features custom shelving and a wet bar, an eat-in chef’s kitchen, casement windows and a woodburning fireplace. There’s also a formal dining room overlooking a courtyard.

Rhinelander Stewart is the granddaughter of William Rhinelander Stewart Sr., who commissioned architect Stanford White to design Washington Square Park’s arch.

The listing brokers are John Burger and Lauren Elizabeth Bankart of Brown Harris Stevens.