A bag of the type that millions of mums have said a silent thank you for will be sold later this month.

So what’s the big deal?

The mum for whom it was first made was Jane Birkin.

The bag carrying her name is now a legendary fashion accessory; perhaps the most consistently sought-after and valuable in history.

You’ll find a million copies and lookalikes, but to be a real Birkin it has to be Hermes.

Jane Birkin with the bag created for her, the sale of which will be a once-in-a-lifetime event for luxury handbag collectors. Image from Sotheby's.

Jane Birkin - the English-born actor and musician who spent much of her adult life in France - was flying with her daughter Charlotte one fateful day in 1985.

Sharing the plane with her was Hermes director Jean-Louis Dumas.

And, Jane had a story that many of us will recognise.

Travelling with kids was a nightmare. She needed a big, practical bag to carry everything she needed.

Hermes had been making luxury accessories and leather goods - many of them equestrian - since the 1830s.

The birth of their handbag range foreshadows the birth of the Birkin: the wife of the firm’s head couldn’t find a good quality leather bag, so they started to make their own.

And they knew how to make stardom work for them. The most famous Hermes bag before the Birkin was the Kelly, named for Hollywood star and Princess of Monaco Grace Kelly.

Grace Kelly also has a Hermes bag named for her.

M Dumas took up Jane Birkin’s challenge.

The triumphant result is still with us now.

Because women absolutely love it.

There are waiting lists, and sales are controlled to tackle hoarding and reselling.

That’s for the new bags.

There’s a more than lively secondary market - perhaps comparable with the luxury watch market - with some standout models going for huge figures.

In 2022 a special-edition Himalaya Birkin made with crocodile leather with diamond and gold hardware made $450,000 at auction.

This is what a $450,000 Hermes bag looks like, in crocodile leather with white gold hardware. Surely the first Birkin will surpass it.

But even a standard Birkin should resell for around $20,000 in the right condition.

How about the first one?

On June 26, in Paris of course, we’ll find out.

The bag that Dumas produced and named - with her permission - for Birkin is being sold.

It’s not quite a standard Birkin.

The size is slightly different from what became the norm. Other design and material details were altered on the way to mass production.

And most bags don’t come with Jane Birkin’s nail clippers attached to a strap inside and marks where she stuck stickers supporting the causes she loved.

This is a unique, single item that sparked a legend.

Birkin took her bag everywhere.

Sotheby’s head of handbag and fashions, Morgane Halimi said: “There is no doubt that the Original Birkin bag is a true one-of-a-kind — a singular piece of fashion history that has grown into a pop culture phenomenon that signals luxury in the most refined way possible.”

This single-lot sale, with no published estimate, is likely to be a once-in-a-generation opportunity for bag collectors.

There aren’t really any benchmarks.

Certainly there are well-known women in the public eye with resources who one can imagine coveting this landmark bag.

Its original owner, who died in 2023, has some substantial artistic achievements in her history. But this luxurious, down-to-earth, beautiful, practical bag is part of her legacy too.

See you in Paris on June 26.