I'm almost dreading the first person to recognize him because I once joked that it should be Cid and that Nero should be there at the time, completely unfazed and unsurprised...but now I love the idea, lol.
ALPHINAUD
This is our new ally: Shadowhu--

CID
Gaius!? You... You're... but h--

NERO
Hey.

GAIUS
<lifts right hand slightly in half-hearted wave>
If for nothing else than that the idea Nero could have pulled Gaius out of the fire only to never bring it up ("because you never asked") is just so in line with his character and the style of smug comedy he exudes.