A five-day exhibition to precede the largest-ever auction of Audrey Hepburn’s private possessions will open at Christie’s auction house in London on Saturday, with some of its most enthusiastic visitors expected to be the late actor’s growing fanbase of teens and millennials.

“An extraordinary migration has taken place,” said Sean Hepburn Ferrer, Hepburn’s eldest son. “Now, 50% of her fanbase are teens and tweens. She has replaced James Dean on that closet drawer in kids’ bedrooms. It’s quite extraordinary.

Photographs of Audrey Hepburn by Cecil Beaton. Photograph: Alastair Grant/AP

“I can only explain that by saying that children are very instinctive and, in a world of a lot of smoke and mirrors with social media, I think they feel there is something very real about her.”

Looking around the spotlit exhibition, it is perhaps no surprise that Hepburn should appeal to those who have discovered her on the very visual world of the internet.

A colourless paste tiara from the film A Nun’s Story. Photograph: Alastair Grant/AP

There are almost too many highlights with Tumblr and Pinterest currency to list, such as the image of Hepburn sitting beneath a shiny hooded hairdryer on the set of Sabrina in 1954, wearing a simple white shirt and black trousers, and the 1957 Bud Fraker photograph in which she is clad head to toe in black, her slender frame curved to one side like a painter’s brushstroke.

Many of the clothes feel as modern today as they were in the 1960s. There are the little black dresses for which she was so famous, such as the feather-trimmed Givenchy cocktail frock from 1968; the Burberry macintosh and heritage checked skirt suits; the 1967 shearling jacket worn in Wait Until Dark; the 1960s coats with their clean, classic lines; the pristine Louis Vuitton luggage.

But while the style feels contemporary, the flawless condition in which they appear speaks volumes about their owner’s values. “She kept them in the closet in Switzerland,” said Luca Dotti, Hepburn’s younger son, by her second husband, psychiatrist Andrea Dotti.

A scene from Breakfast At Tiffany’s, 1961. Photograph: Paramount/Kobal/Rex/Shutterstock

“She was very attentive, a girl out of the war. When Valentino used some of her pieces in an exhibition, he wrote her a note saying: ‘All the others are stained and ruffled up and yours are as good as new’ and she was very proud of that.”

The most worn-looking items are perhaps the most evocative: several pairs of ballet pumps in fondant-fancy colours, with bulges and grooves in the leather marking out the shape of her toes in a way that feels extraordinarily intimate.

A monogrammed powder compact from the 1950s, expected to fetch £2,000 to £3,000. Photograph: Rex/Shutterstock

Those shoes are being sold in lots of three pairs, with estimates of £6,000 to £9,000, so it is unlikely that Hepburn’s youngest fans will get a look in. But, says Ferrer, there are small pieces starting at £100 which, he says, “it is my wish” young fans will acquire.

A selection of Hepburn’s signature ballet shoes. Photograph: Alastair Grant/AP

“I have long discussed this with Christie’s – to try to keep some of the lots light enough that some young girl can try to have something that belonged to her without having to go to the bank and take an advance on their college loan,” he said.

Sharing his mother’s legacy with the world “in the spirit of the keepsake you might receive when you lost a grandparent”, was the auction’s intention, he added.

Letting go of Hepburn’s possessions, which Ferrer said “as a normal family without a chateau” they did not have space to keep, 25 years after her death has clearly been an emotional process.

Ferrer talks of “complex tax situations” and points out that, though the proceeds are going to the brothers on this occasion, they have spent so much of their lives doing charity work in their mother’s honour that giving back has been their life’s work “regardless of how you slice it”. Dotti describes Christie’s staff as “shrinks” as much as organisers.

The behind-the-scenes machinations are unlikely to matter much to Hepburn’s youngest fans, for whom her image is an obsession. “I think she was the first true teenager,” said the exhibition’s creative consultant, Meredith Etherington-Smith.

“She came up in the 50s, when girls looked like their mothers after the age of 16, all trussed up. But she dressed very simply. She dressed like a ballet dancer, actually,” she said.

Hepburn’s feather-trimmed Givenchy dress (centre). Photograph: Rex/Shutterstock

Through her image, said Etherington-Smith “she is immortal. People still want to look like her. Short hair, strong eyebrows, wonderful ballet shoes. What does that sound like? That sounds like today.”

Dotti said Hepburn “would be amazed” by her teenage fanbase, but she would not want to be considered an icon. “She would have hated that word. By its definition an icon is an object of devotion without life and she would have hated both the aspects – being an object and, especially, being without life.”