Years ago, in college, I met the perfect woman. Or perhaps a man’s idea of the perfect woman. She had flawless and dewy skin, angular cheekbones, a cinched waist, milkmaid breasts, long legs, dove-like hands, lush long hair. Wherever she went, people swiveled their necks and stared. She was a fantasy, a vision. A goddess.

And she was miserable.

It emerged that the source of her pain was a secret that she kept until she enrolled in a radical gender studies class. Inspired, she came to terms with her identity, and in the telling she liberated herself. Her secret was that she wasn’t technically female. She had a condition known as androgen insensitivity syndrome (AIS). She was the perfect woman on the outside, and inside she felt perfectly female. But she was genetically male (XY).

Her story was typical for women with complete AIS. At birth her doctors didn’t notice any difference in her genitalia. In high school she went from being a normal girl to an Amazonian queen. She was not only taller than her peers but curvier, too (some androgens are converted to estrogen which act on breast tissue). Unlike other girls, she never got acne or grew pubic or armpit hair (androgens regulate hair growth). She had no body odor. She got recruited as a runway model, was attracted to men and had many boyfriends (including a celebrity), and had sex, albeit painfully. But by age sixteen she didn’t get her period, so her mother brought her to the doctor and an astonishing discovery was made. She had undescended testes. Inside, she appeared male: no fallopian tubes, no uterus, no ovaries.

This gorgeous college student had complete androgen insensitivity syndrome. Women with this condition — approximately 1 in 20,000 — tend to be exceptionally tall and striking in appearance. AIS is caused by a recessive variant of the gene that codes for Androgen Receptor. Because the body is insensitive to the androgen testosterone, the usual male features — penis, testes, scrotum, etc. — are unable to develop. The default phenotype is female, so people with AIS have a vagina or “vaginal pouch” (although most AIS women require surgical expansion). If a woman with AIS were to get a blood test, her testosterone levels would be as high as any man’s, but her body can’t process the hormone. That’s why women with complete AIS are so feminine — arguably more so than other women. (Some people with AIS have only partial androgen insensitivity. Considered intersex, or hermaphrodites, they fall all along the spectrum between typically male and female and have a micropenis. Naturally, there’s much controversy about gender assignment at birth and estrogen or testosterone injections at puberty.)

Several women have revealed they have complete or partial AIS, including singer Eden Atwood and tennis player Sarah Gronert. Although impossible to confirm, several famous celebrities of the past are purported to have had AIS: Wallis Simpson (Edward may have given up the crown for her, but it is said they could never have sexual relations), Queen Elizabeth I, and Joan of Arc. Rumors of AIS abound, perhaps out of jealousy, whenever a celebrity is statuesque, beautiful, and lacking a biological child — Jamie Lee Curtis, Ann Coulter,and even Gisele Bunchen,among many other model types.

In a sense, complete AIS flies in the face of the evolutionary theory I write about in BLONDES. If straight men are drawn to slim waists, shapely breasts, lush scalp hair, sparse body hair, long legs, and flawless skin because those qualities represent high fertility, then AIS is the ultimate deception. As gorgeous as an AIS woman is, there’s no chance of conception. But this ultimately doesn’t matter. It’s the 21st century, and an important lesson must be learned: Femininity is about more than reproduction.