You have seen her face a hundred times before. Peering out of Toulouse-Lautrec\'s iconic Montmartre posters, Jane Avril\'s pale features, marmalade hair and lithe, subtle limbs have become a kind of shorthand both for Lautrec\'s best work and for the whole frenetic glamour of bohemian Paris in the decadent 1890s. Lautrec painted Avril again and again, not just in the black stockings and frou-frou skirts of her day job but also in the quiet, mysterious dignity of her off-duty life. A new exhibition at the Courtauld Gallery in London explores the friendship between Henri de Toulouse-Lautrec and his muse Avril, which created some of the most famous images in European art. In 1893 Lautrec produced a poster to advertise Avril\'s performances at the Jardin de Paris, a fashionable dance hall in the gardens of the Champs-Elysées where le tout Paris, including the Prince of Wales, gathered for sophisticated fun. Article continues below Avril, though, wasn\'t your standard cancan artiste. There were plenty of those available to Lautrec — La Goulue (the Glutton), for instance, or Nini les-Pattes-en-l\'air (Nini Legs-aloft) — but it was to Avril he returned again and again, mesmerised by her unique mixture of sensuality and ethereal detachment. Lautrec\'s friend, Paul Leclercq, came closest to describing Avril\'s appeal: \"In the middle of the crowd, there was a stir, and a line of people started to form: Jane Avril was dancing, twirling, gracefully, lightly, a little madly; pale, skinny, thoroughbred, she twirled and reversed, weightless, fed on flowers; Lautrec was shouting out his admiration.\" It was this off-kilter quality that Lautrec caught so well in The Jardin de Paris. While on the one hand the image can be read as a straightforward piece of advertising, enticing punters into a place of risqué entertainment, but there is also a melancholy undertow. Avril\'s facial expression is unfathomable, while her torso seems contracted and her arms struggle to hold her skirt. Contemporary critics agreed that this painting was a perfect portrayal of the dancer\'s \"inexpressible strangeness\", rendering her not so much as an object of uncomplicated desire as \"a sad and painted large bird\". The poster was an instant hit, and Avril credited it with launching her stage career. It also cemented her friendship with the diminutive Lautrec, who found in her palpable oddness a correspondence to his own physical defects (a childhood accident meant that he never grew more than 4-foot-6). That, though, was where their similarities ended. For, in contrast to Toulouse-Lautrec, who was from one of France\'s oldest noble families, Jane Avril was the daughter of a courtesan. Born Jeanne Beaudon in 1868, she took the stage name Jane Avril because it sounded English, and therefore the dernier cri in chic. At the age of 13 she ran away from home to escape a toxic combination of poverty and abuse, and the following year became a patient at the gloomy gothic fortress that was the Salpêtrière psychiatric hospital in Paris. Exactly what was wrong with her isn\'t clear but her symptoms included nervous tics and hysterical limb-thrashing. It was at one of the bals des folles, the fancy-dress balls that the hospital organised for its patients, that she took her first dance steps and found both her cure and her vocation. Some of those nervous mannerisms found their way into Avril\'s performance style, which one observer described as being like an \"orchid in a frenzy\". At the age of 20 she was taken on by the Moulin Rouge, where her experiences in the Salpêtrière helped shape her public persona as a performance artiste. She was not only known as La Mélinite, after a kind of dynamite, but also as L\'Etrange (the Strange One) and Jane la Folle (Crazy Jane). At the Moulin Rouge is one of Toulouse-Lautrec\'s most frequently reproduced paintings. It serves as the artist\'s homage to the celebrated nightclub and to the circle of writers, artists and dancers who gathered there every night after the rest of the city had gone to sleep. Shown from the rear, Jane Avril is recognisable by her red hair. La Goulue is seen with raised arms in the background. If you look carefully at the middle distance you can make out the diminutive figure of Lautrec, posed for almost comical effect next to his beanpole of a cousin. The pallid face of May Milton, an English dancer and Avril\'s best friend, looms into the canvas from the right. Lautrec, though, wasn\'t simply interested in Jane Avril as a denizen of the demi-monde, that shadowy half-world of dancers and their \"friends\", which came out to play at night. He was fascinated too by her as an individual working woman, one who was required to combine the high glamour of life on stage with the ordinary routines of everyday city living. Jane Avril in the Entrance to the Moulin Rouge shows Avril on the cusp of these public and private worlds. A carriage is glimpsed in the background while the hat and coat on the wall hint at her many male admirers. However, she seems withdrawn and far older than her 22 years, suggesting that this double life is already beginning to take its toll. In Jane Avril Leaving the Moulin Rouge the mood is equally ambiguous. Avril is shown as an elegant but solitary figure. At first glance she could be any well-to-do Parisienne hurrying to get to her next appointment. She appears independent and unapologetic, her upright pose commanding more attention than that of the hunched figures in the background. This autonomous quality was immensely attractive but it also cemented her status as an outsider. As one contemporary remembered: \"She was proud. She didn\'t know how to cry, nor beg, nor apologise.\" Although Lautrec\'s images of Jane Avril appear to be done at speed (you can often see the drips of the paint and the broken vertical dashes where the background has been quickly sketched), in fact they were carefully conceived. Lautrec would call on Avril at any time of day or night and demand a sitting. Often, before the painting session began, he would take her to eat or drink in the restaurant Bagnou, or at the Cabaret du Père Lathuille, where he would study her gestures and expressions intently. At times the painter would even cook for her in his studio, pressing on her the lethal cocktails that he mixed with all the skill of a professional barman. So it is a surprise to learn that Jane Avril and Toulouse-Lautrec never became lovers. Instead, Avril remained what Lautrec needed even more, a loyal friend. Pursued by his demons and hating the physical handicap that excluded him from the outdoor country pursuits he loved so much, Lautrec started to drink heavily. It was, finally, alcoholism that killed him in 1901 at the age of just 36. He left behind him, though, the most extraordinary body of work, images of Montmartre at its glamorous, most seedy best. Much of their appeal was thanks to the extraordinary figure of Jane Avril, the cancan dancer who was so much more. One final image tells us all we need to know about her extraordinary presence. Mostly Lautrec painted Avril from fleeting and oblique angles, as if she were always on the point of eluding him. Here, though, the frontal pose means that we can, for once, look steadily at her pinched white complexion and jolie-laide features. What we see is not a generic Montmartre \"type\" but an individual woman, intelligent and alert. It is her gaze that really holds you. For Jane Avril stares out at Lautrec (and us) with the confidence of one who knows that she is, in her own way, an artist too.