Caster Semenya has lost her case against athletics' governing body the IAAF in the Court of Arbitration for Sport (CAS).
The decision announced by CAS on Wednesday, means that the double Olympic champion will be forced to reduce her natural levels of testetorone to compete in distances from 400m to the mile.
The panel of three CAS judges ruled 2-1 that the International Association of Athletics Federations (IAAF) regulations are necessary to ensure fair competition.
The IAAF welcomed the CAS decision expressing gratitude "for its detailed and prompt response to the challenge made to its Eligibility Regulations".
Last April, the IAAF issued Eligibility Regulations for Female Classification requiring female athletes with testes or naturally high concentrations of testosterone to reduce their levels sufficiently to be able to compete at distances between 400 metres and a mile.
In this landmark judgment, CAS says the IAAF's proposed rules on athletes with "differences of sex development (DSD) are discriminatory but "such discrimination is a necessary, reasonable and proportionate means of achieving the IAAF's aim of preserving the integrity of female athletics in the Restricted Events."
Speaking at the Australian Olympic Committee annual general meeting in Sydney IOC President Thomas Bach said the IOC accepts the CAS decision, and he expressed "sympathy" for Semenya: "I must say, I have a lot of sympathy for Caster Semenya being in this position. The issue such as this is extremely complex. It has scientific impact, it has an ethical impact. It has the impact of fair play in the competition. So it's extremely delicate and extremely difficult."
Following the ruling, the International Olympic Committee (IOC) said in a statement: "We have taken note of the CAS decision in this case and recognise these issues are complex. The IOC is currently working with a group of experts on the creation of guidelines to help International Federations shape sport specific policies and regulations in relation to fairness, safety, inclusivity, and non-discrimination on the basis of gender identity and sex characteristics.”
The ruling would force Semenya to start taking medication to lower her testosterone level within one week if she wanted to defend her 800m title at the World Championships in Doha in September
South Africa's superstar reacted with a tweet saying sometimes "it's better to react with no reaction".
In a statement released by her lawyers the 28-year-old added:
"I know that the IAAF's regulations have always targeted me specifically. For a decade the IAAF has tried to slow me down, but this has actually made me stronger. The decision of the CAS will not hold me back. I will once again rise above and continue to inspire young women and athletes in South Africa and around the world."
Semenya has 30 days to appeal the CAS ruling at the Swiss Federal Tribunal but she could also take the case to the European Court of Justice.
She has always insisted she just wanted "to run naturally the way I was born".
"It is not fair that I am told I must change. It is not fair that people question who I am." - Caster Semenya
Athletics South Africa (ASA) called the decision "disgraceful" and said it will meet soon to discuss the next steps.
"ASA respects the CAS decision and will now review the ruling and decide whether to consider the option of taking this matter to the Swiss Federal Tribunal within the 30 days as stipulated in the ruling," it said in a statement.
South Africa's government ensured Semenya of "continued support as we navigate the future with her" and promised to lobby through other international organisations.
A late entry in Diamond League opener
In a surprising move Semenya was added to the 800m field at the Diamond League opener in Doha just one day before the meet. It is expected to be her last meet before the new testosterone rules go into effect.
The 800m race on Friday evening in Doha will feature all medallists from last year's world championships and the 2016 Rio Olympic Games.
Support from her rivals
Semenya has also received support from her nearest rival over 800m, Francine Niyonsaba.
Speaking exclusively to Olympic Channel, the Rio 2016 and 2017 World Championship silver medallist from Burundi opens up about her tough career start, her dreams for Olympic glory and the medical data hack. She claims the new IAAF regulations are "about discrimination".
What was the IAAF proposing?
The IAAF had argued that "high levels of endogenous (internally-produced) testosterone can significantly enhance their sporting performance" citing "broad medical and scientific consensus".
"The revised rules are not about cheating, no athlete with a DSD has cheated, they are about levelling the playing field to ensure fair and meaningful competition in the sport of athletics." - IAAF president Sebastian Coe
They stated that "7.1 in every 1000 elite female athletes in our sport have elevated testosterone levels" with the majority in track events at distances ranging from 400 metres (including hurdles) to a mile.
The policy says any runner with a Difference of Sexual Development (DSD) resulting in high testosterone must take medication, eg. hormonal contraceptives, to bring it below the 5 nmol/L limit for at least six months.
That level must be maintained continuously thereafter for the athlete to be eligible for competition.
Most females have blood testosterone concentrations between 0.12 and 1.79 nmol/L.
These new rules were approved by the IAAF Council in March 2018 and scheduled to take effect last November.
But Semenya quickly voiced her opposition to the measures and took her case to sport's supreme independent arbiters, CAS.
What next for Semenya?
With no indication of how CAS would view her appeal, Semenya looks to have been preparing for every eventuality.
At last week's South African Championships, she chose to run the 1500m and the 5000m, an event not subject to potential testosterone-reduction measures.
Semenya took the step up in distance in her stride, producing a devastating finishing burst to win in 16:05.97 to win her first ever 5000m title.
The next day she won the 1500m too.
The ruling could also have major implications for her track rivals, and across other sports.
Breakthrough and gender test
Semenya was thrust into the limelight at the 2009 World Championships in Berlin where she claimed her first global title at the age of 18.
The teenager was forced to take a gender verification test and barred from competition.
The IAAF eventually cleared her to race against women 11 months later, saying, "The process initiated in 2009 in the case of Caster Semenya (RSA) has now been completed."
While not confirmed, that "process" is believed to have been a course of testosterone-suppressing medication.
In 2011, the female Hyperandrogenism Regulations came in effect with Semenya taking silver behind Russia's Mariya Savinova at the Daegu World Championships and London 2012.
That was upgraded to gold in 2017 after Savinova was recorded on video admitting to taking anabolic steroids.
But Semenya's performances were well below her best in the period up to 2015 when the hyperandrogenism regulations were suspended.
Chand's fight to compete
Indian sprinter Dutee Chand went to CAS after the Athletics Federation of India had declared her ineligible to compete in the 2014 Commonwealth Games due to the IAAF's hyperandrogenism regulations.
She won her case in July 2015 with CAS suspending the IAAF's Hyperandrogenism Regulations for two years, concluding there was not enough evidence to support the theory that high levels of endogenous testosterone enhanced athletic performance.
Chand's story is told in the Olympic Channel documentary series 'Foul Play'.
The IAAF had two years to come up with further evidence supporting their rules or they would be rendered void.
This allowed athletes with hyperandrogenism to compete without suppression of their testosterone levels with Semenya winning gold in the 800m at Rio 2016.
Chand qualified for her first Olympic Games, going out in the heats of the 100 metres, and spoke to Semenya about her case.
After a number of delays agreed with CAS, the IAAF unveiled their new regulations with testosterone suppression proposed for Semenya's preferred distances but not Chand's sprint events.
Speaking to The Indian Express last April, Chand revealed she had offered Semenya her legal team.
"The first time I met Semenya, during the Rio Games, she made me feel like a close friend. She told me not worry about the case and focus on the sport. She gave me tips on handling the barbs thrown at me.
"I am glad that my battle is over, but hers is not." - Dutee Chand talking to The Indian Express about Caster Semenya in April 2018
Timeline of events
Caster Semenya wins gold at the 2009 World Championships.
Semenya reported to be among athletes who have undertaken gender tests.
The IAAF confirms that gender verification results will be examined by a group of medical experts.
Athletics South Africa (ASA) head coach Wilfred Daniels resigns, citing "negligence" in allowing Semenya to undergo gender rather than standard doping tests.
ASA president Leonard Chuene admits lying about Semenya, insisting his previous denials of knowledge of the gender tests were to protect her privacy.
ASA demands that the IAAF apologises to Semenya for failing to "observe the confidentiality required to handle the matter of this sensitivity" and contravening her human rights.
Semenya prevented from running in an event in Stellenbosch, South Africa, with the IAAF yet to release findings of her gender verification tests.
Semenya cleared to compete again 11 months after claiming the world title, winning two minor races in Finland.
Semenya breaks two minutes for the first time since the controversy at the ISTAF meeting in Berlin where she took World Championship gold a year previously.
IAAF announces new eligibility regulations requiring women with hyperandrogenism to take medication to lower their testosterone levels.
CAS rules in favour of Indian sprinter Dutee Chand leading to suspension of IAAF hyperandrogenism regulations pending further scientific evidence.
IAAF announces updated regulations requiring testosterone suppression for female athletes competing at distances from 400m to a mile to take effect from November.
Semenya goes to CAS to challenge proposals with IAAF delaying implementation pending CAS decision.
CAS postpones ruling to late April.
IAAF confirms it hopes to have regulations in place for 2019 Doha World Championships.
May 1 2019
CAS publishes decision - Semenya loses appeal against IAAF.