Trivia: During Borden's performance which ends with Angier shooting him, on at least two occasions the bill for the show can be seen off to one side. About halfway down is the name "Harry Dresden", the name of the wizard protagonist from the Dresden Files book series by Jim Butcher.
Trivia: The "Chinaman" in the movie was based on a real-life magician. He wasn't Asian at all, he just dressed and lived the part. The first English he ever spoke in his career were his last words. When a bullet catch went awry, he uttered the words, "My God, I've been shot" just before his death.
Trivia: There are a couple times in the movie, where if you listen carefully, you can hear Angier's English accent slip through (such as when he says to Olivia "He lives his act"). These are subtle clues to the later revelation that Angier is a British aristocrat pretending to be an American magician.
Answer: Angier always wants to take revenge on Borden as he is the reason behind the death of his wife. He knows that Borden is in the crowd the two times, first time, Olivia suggests Borden to watch the new "Transported Man" trick of Angier, where Borden finds out the trap door in the bottom of the machine, second time, Borden wants to know how Angier flies that distance with in seconds through the trap door. As expected by the Angier in the final play, Borden reaches the back stage where actual Angier is drowning (it is as always actual Angier drowns and the replica of Angier appears at some distance in every performance). So, as per the plan the replica hides to create an impression that Borden intentionally murders Angier. Note: the replica of Angier has the same ability and sense like actual Angier.
Rajesh v
It's never stated whether the "real" Angier drowns or takes the bow, but it's implied that it doesn't matter - as the clone is a perfect copy, they are both "Angier." Angier at one point says, referring to toll the trick has taken on him, that each time he did it, even he himself didn't know whether he would be the man in the box or the prestige. Similarly, when Angier asked Tesla which hat of all the duplicates was his, Tesla replied "They are all your hat."