The young athlete, now competing at the Rio Games, always considered herself to be a girl just like the others, a girl who loved to run. Then the governing body of track and field told her she was different, so different that her track career could be over.
Marked "confidential" and signed "best sporting regards," the letter outlined a choice for the athlete: Open herself up to a panel of medical experts who could recommend surgery or chemical treatment to reduce her testosterone levels, or stop competing.
She had fallen foul of the International Association of Athletics Federations' rules aimed at providing a fair playing field for women by keeping out athletes with high testosterone, a naturally occurring strength-building hormone.
Writing to the man who ran track and field in the athlete's country, the IAAF's medical director at the time explained that blood and urine tests detected testosterone levels that were "abnormally high" for a woman.
The suspected cause, wrote Dr. Gabriel Dolle, wasn't doping but another hot-button issue in athletics that is likely to flare in this final week of the Rio de Janeiro Olympics: hyperandrogenism.
Had the athlete not been a runner, she might never have known of her condition. It was flagged by the IAAF's tests that look for banned drugs. She was stunned and uncomprehending when told that her testosterone pointed to hyperandrogenism, her then-coach told The Associated Press.
"She couldn't understand. It was shock," the coach said. "I said, 'You're not alone. There are others.'"
Thus started a months-long process of medical scrutiny, trips to foreign clinics for batteries of tests, and potentially life-changing choices shrouded in medical secrecy that makes it hard to investigate the IAAF's treatment of hyperandrogenic women.
The AP will not name the athlete, the country she is competing for or give details, including racing achievements, that could help identify her. In messages with the AP, she said she is focusing on competition and that her story is "personal and private."
Another athlete has become the unwilling face of this complex and excruciatingly sensitive issue. Caster Semenya will race in Rio and likely win gold in the 800 metres. Believed to be hyperandrogenic, outed as physiologically different without her consent when she won the world championship 800 in 2009, the South African's dominance has again pushed to the fore divisive questions about whether allowing women to compete with testosterone levels far above the female norm is fair and whether the hormone's attributed performance-enhancing effects are significantly greater than other natural gifts, like height for basketball players or big feet for swimmers.
Semenya first races Thursday. The IAAF letter and the exclusive AP interview with her former coach, who was intimately involved in her eventual decision to agree to testosterone-curbing treatment, shed unprecedented light on the inner workings of the IAAF process that at least 14 women have gone through.
It is not publicly known how many hyperandrogenic women are competing in Rio. But a study published in 2014 by Dolle and other medical experts calculated that seven out of 1,000 elite female athletes may be hyperandrogenic, 140 times higher than expected among the general population. Hyperandrogenism is a medical condition which causes a person to produce high levels of hormones and can be caused by differences in sexual development.
Having not withstood a legal challenge brought by another female athlete at the Court of Arbitration for Sport, the IAAF regulations are now on hold, suspended by the CAS since July 2015. That means hyperandrogenic women can compete in Rio without having to artificially control their testosterone levels.
The CAS case was brought by Dutee Chand, an Indian sprinter who challenged the rules after she was suspended, and who, like Semenya, saw intimate medical details become fodder for public debate.
"God wanted to bring a change (in the rules) through me," Chand told AP before competing in 100-metre qualifying on Saturday. Speaking as fast as she runs, her nails painted red and black studs in her ears, the petite sprinter said she has put her ordeal behind her, is relishing the Olympic experience and longs to meet Usain Bolt.
"By the time I came to know about my problems, the issue already was out in the open," the 20-year-old said. "Everyone supported me. I don't worry about what has happened in the past."
The coach who spoke to AP praised Chand's resistance against the IAAF rules, saying: "Thank goodness that there were courageous people who protested."
The AP will not identify the coach to avoid identifying the athlete. As her confidant during the process, the coach was involved in her decision-making, including choosing hormone therapy instead of surgery to lower her testosterone. The IAAF letter says the coach was present during a meeting with a federation representative when a follow-up sample was taken from the athlete to confirm the diagnosis of hyperandrogenism.
The IAAF letter explaining the medical process facing the athlete was provided to AP by a former federation representative who was involved in the implementation of the hyperandrogenism regulations. The governing body introduced them in 2011 after the furor that followed Semenya's world title in Berlin. There was widespread criticism of track officials' handling of her case, including leaking without her consent that she had undergone sex testing. "I have been subjected to unwarranted and invasive scrutiny of the most intimate and private details of my being," Semenya subsequently complained.
The AP's source said the IAAF regulations were ensnaring athletes from developing countries with little education or the financial means to contest the rules, and forcing them to either accept medical treatment or stop competing. The AP is not naming the former federation official because he wasn't authorized to release the letter.
During the IAAF process, the athlete could not compete. The coach explained her absence by lying that she was injured.
The first IAAF-requested tests to determine the exact nature of her condition required a trip to another nation's capital, where she was met by Dolle. That was followed by two trips to a clinic in Nice, France, all paid for by the IAAF, the coach said.
The first Nice trip was accompanied but the second, lasting over a week, was not because the IAAF did not want to pay for someone to go with her, said the coach.
"I didn't want her to go alone. She didn't speak French very well. I was afraid she wouldn't understand," the coach said. "I said, 'Before you take any medicine, call me. Don't take anything.' The doctors say, 'It's for her good.' And I thought to myself, 'She's fine as she is.'
"...They said, 'We're doing tests to help you.'" Maybe they gave her details but she didn't understand. She just knew that they were saying she had to have the tests to come back to track and she accepted because that is what they wanted."
After the second Nice trip, subsequent correspondence from Dolle offered the athlete two choices: surgery or medicinal treatment, said the coach. The coach urged her not to go under the surgeon's knife, fearing the irreversible effects.
"I said to her, 'We can't take this risk; cut things off that God gave you,'" the coach said. "When things are cut off, it's forever. You can't get those parts back."
Other athletes consented to surgery. Doctors in Nice reported in 2013 that they operated on four hyperandrogenic women, aged 18 to 21 and from rural or mountainous regions of developing countries, cutting out gonads and partially removing their clitoris. The athletes were told that surgery would most likely dent their athletic performances but allow them to continue competing, the doctors reported. They said the women were allowed to resume competition one year later.
The coach feels the rules discriminated against women because there aren't equivalent rules for men.
"It punishes women because there is no law that bans some men because they are more manly than others," the coach said.
The coach lamented a lack of detailed information from the IAAF about the surgery or medicinal therapy; "you're told just that it is bringing your level down to the level of other women."
"She said, 'Since I love this sport, I'll take the medicine,'" the coach said.
The athlete continued to train while suspended.
"She was desperate to run. She kept saying, 'I'm taking the medicine. Why can't I run?'"
The treatment caused weight-gain and the unpleasant side-effect of making the athlete smell "awful," sweaty and dirty, even though she stayed clean and wore deodorant and perfume, the coach said. The smell vanished when she came off the treatment, the coach added.
The treatment was administered by a doctor in her country who reported back to the IAAF. The treatment did not lead to a huge dip in her running performances.
When the IAAF eventually gave the athlete the green light to resume competing, she was delighted, the coach said. But the CAS only suspended the regulations, rather than overturned them entirely, giving the IAAF until July 2017 to produce evidence that high testosterone gives hyperandrogenic women a significant performance advantage.
"She is free but she is scared that from one day to the next they could stop her from running again," the coach said. "She's in limbo, waiting for something bad to happen. She asks, 'Are they going to stop me again? Are they going to make me take more medicine?"
John Leicester is an international sports columnist for The Associated Press. Write to him at firstname.lastname@example.org or follow him at http://twitter.com/johnleicester . See his work at http://bigstory.ap.org/content/john-leicester
Ashok Sharma in New Delhi contributed.