I think Brad and others gave a little too much credit to the second flashback in Uncharted 4. We found out that Nate isn't related to Francis Drake in Uncharted 3 - that wasn't a big revelation. That is what the subtitle of the game, Uncharted 3: Drake's Deception, refers to (also Francis Drake's deception of where he sailed).
Uncharted 3 also mentioned that his mother committed suicide. The only new information we were given was that his last name was Morgan and that his mother was researching Libertalia.
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