The idea of the boy "E" not knowing his gender is not credible anyways.
Best fiction stories are the ones which start with a true event, with something credible, and from it to develop a whole new scenario different than reality, so readers can fall in the trick.
Most famous fiction stories can start with anything, but famous is not synonymous of best.
However, you don't have to ask any permission to nobody in order to write a fiction story. The LGBT can't obtain such a power over your writings, unless you are using a real boy who fits with the character of your novel and he or his parents are making complaints about it.