I am loitering in a sex museum in Prague. Amidst the chastity belts and pre-war dildos stands this... thing. It looks like an instrument of medieval torture; or a commode for an incontinent Chinese warlord.

Yet it turns out to be something way more bizarre than this - what I am ogling is the fauteuil d'amour, the famous "armchair of love". It's a chair specifically designed by a top French furniture-maker, so an English King could have sex with two or more prostitutes. Looking at the surreal object, it's hard to work out how.

The king was Edward VII: he used the chair when he visited the opulent brothel of Le Chabanais, one of the great bordellos of fin de siecle Paris. Yet the chair in Prague turns out to be a replica. Could the real one still exist?

To find out I take the Eurostar to Paris, and trek to Le Chabanais in the 2nd arrondissement. In its heyday, the sober facade of this inner-city townhouse hid a riotously ornate interior - a world of mirrors and velvet, where beautiful trollops would stand bare-breasted on pedestals, for the delectation of the wealthy punter.

All this was swept away in 1946, when Le Chabanais, and the other "tolerated houses", were abolished in a fit of post-war puritanism. The madams, the girls and their clients were scattered. But what happened to the famous fixtures; what happened to the chair?

In the modernist towers of the Bibliotheque Nationale I consult the records. They tell me that the armchair of love miraculously survived La Fermeture [the closing], and was bought at auction in 1946 by an industrialist. The chair was then resold at Drouot, another Parisian auction house.

A metro ride takes me there, but when I ask the girl at reception about "the English king's oral sex chair" (try saying that in French), she has a fit of giggles. Finally she confirms that the chair went under the hammer for a third time.

"Herve Poulain," she tells me, "auctioned the armchair in 1996." Eventually I track down M Poulain in his office. After some cajoling, he calls "a certain client". Then he turns, and smiles: Oui, the chair survives.

Huzzah! I have one more question. Is the chair still... used?

"Naturellement."

I haven't the guts to ask how.