With all eyes turned towards next month's sale of Monroe's estate in New York, a smaller auction in London last Monday went almost unnoticed.
In the sale of vintage film posters at Christie's, a lobby card poster of Hepburn's 1961 film Breakfast at Tiffany's, signed by the actor, made pounds 1,265 against an expected pounds 400-600.
Of posters featuring Monroe, only two, for Some Like It Hot, made as much, although they were unsigned. Unsigned posters of Breakfast at Tiffany's, of which around 300 of the original 8,000 printed in America still exist, were estimated at pounds 250-600. One broke the pounds 1,000 mark.
"Audrey Hepburn is enormously collectable," Sarah Hodgson, Christie's head of rock and pop memorabilia, said.
Last year, a family photo album and correspondence between Hepburn and her father sold in London for more than pounds 70,000, 10 times the expected price. Both lots were sold to the same anonymous foreign buyer.
Hepburn, who died of cancer in 1993, was the antithesis of the blonde, curvaceous Monroe. Dark, gawky, with a style all her own, she starred in a host of films and became closely associated with the fashion house Givenchy, whose clothes suited her frame.
She first came to public attention in Roman Holiday in 1953, going on to make Sabrina, My Fair Lady, and Funny Face. As Holly Golightly in Breakfast at Tiffany's, she charmed everyone bar Truman Capote, who hated the adaptation of his novella.
Her slender good looks have been envied ever since. In Japan, young women are reported to have spent large sums of money on cosmetic surgery to be given the distinctive Hepburn-style cheekbones.
Hepburn is one of a small number of big-name actors who have attracted increasing interest from memorabilia collectors in the past 15 years.
Ms Hodgson said: "The Hollywood greats are always going to be sought after - Monroe, James Dean, Greta Garbo, Marlene Dietrich and Audrey Hepburn."
Many posters can command thousands - one for the 1932 American horror film The Mummy, starring Boris Karloff, made more than pounds 280,000 a couple of years ago. American Hitchcock posters are particularly sought after. Last Monday's sale included more than 100 from the director's films.
Rarity and condition are factors in the value. In the past, posters were normally ditched at the end of the cinema run. The record-setting poster for The Mummy was one of only two known copies.
However, the sale of the remaining estate of Monroe provides a different type of excitement, a glimpse that goes behind the image.
The sale will include Monroe's script of Some Like It Hot, along with her personal clothes, and books and accessories, as well as the ring from her marriage to baseball great, Joe DiMaggio. "It's the last sale of the millennium of this magnitude," Ms Hodgson said.Reuse content