Unfortunately, I don't remember the name of the star of this story, but I'm told that there was a notable mathematician who believed the Perfect Graph Conjecture to be false and spent many years trying to prove it one way or another.

Meanwhile, another mathematician (presumably László Lovász) announced that he had found a proof (in the affirmative).

Upon hearing the news that the open question had been resolved, the first mathematician was able to produce a proof within 90 minutes.

Once again showing that it's much easier to do something once you know it can be done.