I MET her in Copacabana. She was tall, with toffee-coloured skin, long, black hair and a bosom that could have smothered Corcovado. She was wearing designer sunglasses, which perched upon her thin nose over protruding bee-stung lips. I can describe her appearance, but not her aura: on the beachfront with the highest concentration of gorgeous women and muscled men per square foot, she outglamoured them all.

Emilio, my Brazilian friend, nudged me. “A travesti,” he pronounced, with an air of seen-it-all-before.

I wasn’t so sure.

“Maybe post-op,” he continued. “You only have to look at her. Hormones, silicone, collagen.”

I looked at her. There was nothing masculine about her mien. I stared for too long; our eyes locked and she smiled. Emilio waved her over to our table with that natural, instinctive hi-I-want-to-talk-to-you Brazilian innocence. Her name was Alicia, and it soon became clear that a gringo who spoke her language held for her the same exotic fascination that she held for me.

That night we partied together, Alicia and I, in Club W in Ipanema. I observed every nuance in her mannerisms. Like a good dancer, she came in comfortable low-heel shoes and a simple short skirt; it was she, not her clothes, that was flashy, and her vibrant, vivacious behaviour was supremely feminine. After several caipirinhas, I felt brave enough to broach the subject indirectly, as Emilio had advised me.

I told her about a book I’d been reading that described the story of the Chevalier d’Eon. He was a French ambassador in 18th-century London whose gender was the subject of much speculation. And I mean real speculation, because there were bets made on whether he was a man or a woman. To the end, he professed to be a man, but, strangely, he refused to be subjected to a medical examination, and was taken to court by a betting syndicate. After a bizarre trial, the jury decided that he was legally a woman and that he should always dress and behave like one from then on.

“You’re wondering too?” she asked.

Despite my long preamble, I was still embarrassed. “No, I think you’re a woman,” I said. “So beautiful you make both men and women jealous.”

It took her a long time to reply and when she did, she changed the subject: “So what was the end of your story?” “She finished her days in a nunnery in France,” I replied. “On her deathbed, she was examined by two doctors: she was most definitely a man, though she’d been acting like a woman since the trial.”

Alicia laughed, then turned to me: “You don’t want to wait until I die, do you?”

No, I didn’t, and I didn’t have to. That night I took her home, and I did find out. But if it didn’t matter to me, and it didn’t matter to her, then it shouldn’t matter to you.

Unless you want to start taking bets.

John Malathronas is the author of Brazil: Life, Blood, Soul (Summersdale £8.99)