On display, the dresses that defined Monroe

The billowing white dress that Marilyn Monroe wore above the blast of a New York subway in The Seven Year Itch has become legendary in Hollywood costume design. Once exposing a risqué expanse of the starlet's thigh, the infamous frock is one of six outfits by the Oscar-winning costume designer William Travilla to go on display for the first time in 40 years today.

The original dresses are some of the most famous ever worn by the Hollywood bombshell, and until now they have been closely guarded by the Travilla estate. The pink satin gown Monroe wore to sing "Diamonds Are A Girl's Best Friend" in the 1953 film Gentleman Prefer Blondes will be another highlight of the show, running at the Hilton Brighton Metropole hotel in Brighton until Sunday.

For the same film, Travilla himself had sewn the star into a sheer gold dress that is also on display at the exhibit. With its plunging neckline and flimsy fabric, the gown was considered so revealing that it only just made it past the censors.

Enthusiasts for the Fifties film icon will also get the opportunity to see the purple satin number she wore in How to Marry a Millionaire, and the red sequin dress seen in Gentleman Prefer Blondes. But for Travilla, perhaps the most prized dress of all in the collection was a bespoke crepe halterneck that was never intended for a film.

Also on display are a collection of Travilla's preliminary sketches, patterns and designs for the star.

Despite working with scores of beautiful movie stars – Greta Garbo, Judy Garland and Sharon Tate, to name a few – Travilla's Monroe costumes were said to be his most prized. Travilla was notoriously protective of the dresses, keeping them hidden away so that they became known as "The Lost Collection".

The two first met in 1950, when Monroe asked to borrow the contract designer's fitting room at 20th Century Fox. From then on their mutual appreciation grew, and she later autographed a nude calendar of herself for the designer with the words "Billy Dear, dress me forever. I love you, Marilyn."

Their close friendship was another reason why Travilla kept the film star's costumes under lock and key. After she was found dead next to an empty bottle of sleeping pills in 1962, the designer vowed to protect her memory at all costs.

But after Travilla's death in Los Angeles in 1990, the collection was passed on to his partner, Bill Sarris. Sarris now runs Travilla Inc, and wanted the exhibition to be a tribute to the two film legends. An Alzheimer's sufferer, he decided the exhibition should be an opportunity to raise money for the Alzheimer's Society.

"This is what Monroe fans have been waiting for" said Andrew Hansford, of Travilla Inc, who is organising the UK exhibition. "Never before have these items left the Travilla private estate so it's the first time people can get close to Marilyn and experience iconic memorabilia."