Two British athletes born male are on the verge of making history by competing in women's events at next month's Olympic Games, The Mail on Sunday can reveal.
If selected, the unnamed pair will become the world's first transgender Olympians at Rio.
But worryingly for British sports fans, they have revealed they are so fearful of being exposed and ridiculed under the Olympic spotlight, they would 'probably drop back' if they found themselves in a medal-winning position.
Their inclusion in Team GB will be hailed as a remarkable human rights victory - but it will also ignite controversy, with critics arguing that male-to-female competitors have an unfair biological advantage in terms of size, muscle mass and lung capacity.
Delia Johnston, an adviser to several sporting bodies on transgender issues, said the pair have already represented Britain at 'a European championship sporting event'.
She described one of them as a potential Olympic medal-winner, having achieved an 'awesome' personal best earlier this year.
Their gender status is known to the organisations governing their sports but not to rivals from other nations.
The Mail on Sunday can reveal that dramatic changes to International Olympic Committee guidelines have given hope to transgender athletes across the world.
New rules mean they can now take part in the Games without having reassignment surgery.
Instead, competitors born male need only declare themselves female and demonstrate that their testosterone level has been below a specified point for a year.
However, the two Britons transitioned from men to women some years ago and have since 'competed in their assigned gender'.
Their emergence on the international scene was confirmed by Ms Johnston, who has advised the Football Association and UK Athletics, and helped shape policy on transgender issues.
She was also an ambassador at the London 2012 Olympics.
Ms Johnston said their recent performances ought to automatically guarantee them places on Team GB.
'They should be selected but they fear they will be deemed too tricky - too many issues, too much negativity,' she said.
Members of each Olympic team are initially selected by their own sport's governing body. Nominees then go before a British Olympic Association panel to be ratified.
It is not known if the two women have yet been nominated by their sporting bodies.
Ms Johnston, herself a transgender woman who runs an organisation called Trans In Sports, did not reveal the sports the women compete in, adding: 'They transitioned long ago and have competed at a European championship for this country.
'Their national sports federations are aware of their gender history.'
But she warned: 'If they were in a gold or silver medal position they would probably drop back because their fear of ridicule and total humiliation is so massive.'
The BOA is supportive of all athletes - including transgender competitors - who meet the Olympic qualification criteria.
A spokesman declined to comment on whether the two women would be selected for Rio.
However, it is understood the BOA has not yet been made aware they are under consideration.