Board Thread:Questions and Answers/@comment-9826910-20130618064245/@comment-11051098-20130803163613

No, his new Shikai is 2 single-edged blades. But who knows, his new Bankai might become 1 double edged sword or some kind.

@ HollowKing17:

Byakuya seem to be very skilled at hiding it when he's surprised. The only time I've seen him surprised, or shocked, was after Ichigo went into Bankai on Sôkyoku Hill and moved so fast that he was right beside Byakuya with his blade to Byakuya's throat.

I would think that if Byakuya knew the name of Engetsu, he would connect it to Zangetsu, and at the time, he didn't seem to know or guess about Ichigo's heritage. As far as I could see, he only saw Ichigo's resemblance to Kaien, but scuffed it off as a mere coincidence.

Judging by his words to Ukitake on the latter, he had apparently seen Kaien before. We don't know when Kaien was a lieutenant and for how long, we only know that Ukitake tried to make him say yes to the position about 110 years ago. Byakuya saw the resemblance, and that could have been all. But he could also have connected Isshin's disappearance 20 years ago to Ichigo's apparent age (if he knew enough about human evolution to guess his age) and guessed that he could be Isshin's son.