When the fabulously wealthy Consuelo Vanderbilt penned her mischievous and at times malevolent memoirs detailing, in part, her life as Duchess of Marlborough, it was published as The Glitter and the Gold.

By contrast, The Gutter and the Grime might aptly summarise the life in its later stages of Gladys Deacon, her successor as chatelaine of Blenheim Palace, until her bust-up with the duke.

Gladys, like her friend Consuelo, was one of that group of young American heiresses determined to buy their way into the British aristocracy. Edith Wharton gave them a name that stuck in the title of her last novel, The Buccaneers.

In her youth, besides much visiting among the stately homes of Britain, she befriended the likes of August Rodin, Claude Monet and the art collector Bernard Berenson.

Marcel Proust wrote of her: “I never saw a girl with such beauty, such magnificent intelligence, such goodness and charm.”

Fifty years on, though, she was to be found – turning night into day as Proust did (when he got up at all) – living in domestic circumstances of indescribable squalor.

Her biographer Hugo Vickers does his best to describe it in his newly published The Sphynx (Hodder & Stoughton, £25).

This title (to which is added The Life of Gladys Deacon – Duchess of Marlborough) strikes me as perhaps misleading since the name was famously applied by Oscar Wilde to his loyal friend Ada Leverson.

Here it commemorates Gladys as the subject of two lead sculptures – the work of William Ward Willis – on the east terrace at Blenheim.

These, and studies of her famously large blue eyes on the ceiling of the palace portico, the work of portrait painter Colin Gill – the cousin of sculptor, print designer and pervert Eric Gill – are all that remain of her at this grandest of houses from which she was evicted in 1933 by the 9th Duke of Marlborough.

She took up residence at Chacombe Grange where, behind barbed wire and thick black curtains, she lived a life that would have been unthinkable to the Gladys of her prime, her beauty utterly spoiled by the injected wax from a botched ‘nose job’ that had leaked into her face.

Vickers writes: “Sometimes Gladys sat with her feet up, smoking a pipe, the cats clambering over her. She had had all her teeth taken out in 1948 and Andre [her Polish handyman] was astonished when she dropped her false ones, then simply picked them up and replaced them in her mouth without washing them.”

A neighbour, Sue Woodford, said people thought her a witch: “Combinations not unlike those worn by cowboys in old Western films were her ‘undies’ and a cotton wraparound overall on top with a sleeveless leather jerkin (like those coalmen wear) completed her outfit. Her feet were encased in down-at-heel wellingtons which were liberally studded with red-bicycle puncture repair patches.”

Of course, all this could not go on forever. There were very real concerns for her well-being, and the security of her jewellery – it fetched nearly half a million pounds after her death – and valuable pictures.

In 1962, on the night of March 15, the Ides of March, she was forcibly removed and taken to St Andrew’s mental hospital in Northampton.

“Four men in white coats took hold of Gladys,” writes Vickers, “who fought like a wild animal cornered in its lair, and dragged her from the house”

On arrival at St Andrew’s , the matron declared that she could not remember a patient admitted in such a dirty state.

She would remain at the hospital, in which the poet John Clare was famously confined from 1837-64, until her death 15 years later.

For the last two years of her life, she was visited regularly by Vickers, who had read of her existence in the diaries of the politician Chips Channon.

Vickers’s biography was published in 1979, when I was among its enthusiastic – and very surprised – readers. Another was Cecil Beaton, who promptly appointed him his own biographer.

The new edition, which has been completely rewritten, is a fascinating glimpse of a lost world and a highly unusual woman at large, and ultimately adrift, in it.