Thomas Bompard, Head of Sotheby’s London Impressionist & Modern Art Evening Sales and Curator of Actual Size, said: “Picasso has depicted a world on a scale so intimate you can hold an entire artistic vision on your finger. Sometimes the smallest of things can contain a universe of thought and emotion, and so it is with this ring – an intimate piece that allows us a captivating glimpse into secrets that might otherwise not be shared. Picasso conceived this ring just as he was working on his large-scale masterpiece Guernica: one of his greatest art historical achievements coinciding with an extraordinary emotional masterpiece in miniature.”

Of Picasso's many muses, few had as much influence on his artistic career or personal life as the mesmerising and intelligent raven-haired French photographer, painter and poet Dora Maar. Their relationship, though intensely passionate, was far from perfect and went through shifting tides of anguish and callousness. During one promenade along the Pont Neuf, Maar and Picasso had a bitter altercation as the artist reproached his mistress for having prevailed on him to give a work of art in exchange for a cabochon ruby ring. In the heat of the moment, Maar silenced her lover by taking the ring from her finger and hurling it into the River Seine. Later regretting her rash actions, Maar haunted the spot where the riverbed was dredged for several days in hopes of recovering her ring – but it was lost for good. Picasso, ultimately regretting having upset his impulsive paramour so deeply, made a ring designed and crafted by his own hand. The intricate ring bears a portrait of Dora Maar that carries the hallmarks of his most expressive works, yet is charged with the additional intensity and emotion of its genesis. The ring remained in her personal collection up until her death in 1997. Portrait de Dora Maar will now be offered for the first time since the sale of her estate as part of Sotheby’s inaugural Actual Size sale on 21 June, with an estimate of £300,000-500,000.

That a ring should have been at the heart of this dramatic episode is somewhat fitting, as the hands the ring would have adorned were always central to the tempestuous relationship of the two lovers. The legendary story of one of their first encounters sheds light on why Maar’s hands were always a particularly charged motif. Picasso came across Dora Maar seated at a neighbouring table in the fabled Parisian Café Les Deux Magots. Maar was repeatedly driving a small knife between the fingers of her gloved hands into the wood of the table – sometimes missing and drawing blood. Instantly entranced by this dangerous game, Picasso introduced himself and by the end of the evening had asked for the black gloves as a memento.

Quite aside from the intensity of their personal relationship, Dora Maar played a critical part in Picasso’s artistic career. More than just a muse, she was a formidable personality and an artist in her own right, acting as a lively and challenging sparring partner for Picasso. Most importantly of all, perhaps, she was a part of his life during the period of his greatest political engagement – the Spanish Civil War. She was a photographic witness to his monumental mural Guernica, and even painted some of the vertical strokes on the horse in a minor but symbolic contribution. Her features were also introduced into the woman holding up a lamp. In one of his most iconic paintings, Weeping Woman, now in the collection of the Tate Modern in London, Maar’s inner turmoil stands in for Spain’s agony. Picasso’s portraits of Maar were marked by these tortured renderings, as he used her powerful features and radiance to express an unparalleled energy. Maar was forced to make great sacrifices to keep their relationship going despite both of their hot-tempered personalities and the bouts of depression and self-criticism that stemmed from living in his shadow. Indeed, throughout their affair, Picasso continued to see his former lover Marie-Thérèse Walter, mother of his child Maya – contrasting their personalities in almost cruel ways. Then in 1943, Picasso met Françoise Gilot, 20 years younger than Maar and 40 years younger than him. Maar’s state of mind became increasingly unstable as her jealousy mounted and by 1946 their final separation was inevitable. Maar suffered a complete mental collapse, followed by a nun-like seclusion where she focused only on art and religion. Her decision to keep this ring, among other mementos and paintings from Picasso, indicates that her powerful feelings for the artist never truly ceased.

This month, to coincide with its flagship sales in London, Sotheby’s will stage a deceptively ‘small’ sale. Bringing together a range of works from across the 20th and 21st centuries, with occasional surprises from earlier moments, this first-of-its-kind sale will include a broad mix of exceptional paintings, sculptures and works on paper which share one common characteristic – each one will be no bigger than the size of the catalogue page on which it is illustrated, in ‘Actual Size’.