Film-maker Shannah Laumeister, 43, who said the two were secretly married in 2009, confirmed he died at his home in New York on Wednesday.
Stern photographed Monroe for Vogue magazine, just weeks before she died from a drug overdose in 1962.
Other celebrities he photographed included Audrey Hepburn and Twiggy.
Laumeister said: "He'll be remembered as someone who loved women and loved taking pictures and putting things he felt strongly about in the camera.
"His images will live forever and wow generations to come," she said, adding that the Monroe images "go beyond the photograph and become a work of art".
Stern took more than 2,500 photographs of Monroe during the intimate three-day shoot at the Bel Air Hotel in Los Angeles, six weeks before her death in 1962.
The nude and semi-nude images - including several which Monroe rejected for magazine publication - were published in a 1982 book titled The Last Sitting, and a second book, Marilyn Monroe: The Complete Last Sitting, that came out in 2000.
In a documentary about the photographer made by Laumeister, Stern said: "It was a one-time-in-a-lifetime experience to have Marilyn Monroe in a hotel room, even though it was turned into a studio."
A collection of 36 photographs taken during The Last Sitting were auctioned in New York for nearly $150,000 (Â£102,581) in 2008.
Born in Brooklyn, Stern photographed a host of celebrities such as such as Sophia Loren, Elizabeth Taylor and Truman Capote during a career that spanned 50 years.
He was also highly regarded as an advertising photographer, launching his career with a campaign for Smirnoff Vodka.
The image showed a V-shaped glass of vodka set in the front of an Egyptian pyramid.
Along with contemporaries Irving Penn and Richard Avedon, he is credited with transforming commercial photographs into conceptual art. He also took the publicity shots for Stanley Kubrick's 1962 drama, Lolita.
Bruce Barnes, director of the George Eastman House, a museum of photography and film in Rochester, New York, said: "He was an enormously innovative photographer, both as a commercial photographer and a photographer of celebrities and fashion models. And one of the great people in his field."
The museum is preparing to present Stern's only documentary film, Jazz on a Summer's Day, which he made in the late 1950s, about the Newport Jazz Festival.
Stern and Laumeister had been scheduled to attend a screening of Laumeister's documentary in August, Barnes said.
Stern's funeral is due to take place in New York on Friday.
Famed US photographer, Bert Stern, best known for his images of Marilyn Monroe in what became known as The Last Sitting, has died at the age of 83.