This is a great humor diversion.
One thing to remember is that men born with more than two are far more prone to testicular cancer and only a very small percentage of those very few born this way have the third testicle actually working and doing anything.
The removal of testicles is routinely done for several medical reasons including cancer.
Testosterone is produced in the testicles and a small amount is produced in the liver.
The liver will in some cases try to ramp up production as other tissues are removed. While not common in humans this is why some castrated dogs and cats will still exhibit mating behaviors and marking of territories even after castration has been done.