I've done enough mathematical proofs that I don't think I need to "google it", but I read the Wikipedia page anyway. It failed to explain how a mathematical proof could have anything to do with "proving" General Relativity in absence of empirical evidence. He certainly proved that (as I said before) it agreed with existing (experimentally backed) theories using mathematics, but if you have a method which allows you to deduce the truth of physical laws from purely mathematical proofs (no links to experiments at all!) you'll revolutionize epistemology. As it stands most scientists are using the crutch of experimental evidence at some level (either directly or by reasoning within theories that are at least for now validated by experiment).
> Whether or not it was empirically validated is irrelevant. It was true mathematically
If you mean it was a self-consistent theory, note that there are infinite physically incorrect theories which are "true mathematically". It is true mathematically in the same way number theory is "true mathematically", but you don't see anyone assume that we can describe gravity with prime number theory. If you mean it was mathematically proved consistent with previous physical theories backed by evidence, we're back to the experimental link, and also there are infinite physically incorrect theories which would agree with Newtonian mechanics and special relativity. If you mean he proved it satisfied some properties we expect from physical theories because they've been consistently upheld (e.g. energy conservation), there's an infinite number of wrong ones there too.
Mathematical convenience has been an excellent guide in physics, particularly fundamental physics (electromagnetic waves, antiparticles, and the Higgs Boson were all the results of positing things for mathematical convenience), but it is not a substitute for verifying novel experimental predictions. Nobody taken seriously in the physics (or mathematics for that matter!) community thinks it is, not even the often decried string theorists.