BHLDN Catherine Deanne Sian Gown.
I bought this dress online. It's beautiful but not the right size for me. As you can read below, the dress was hemmed but otherwise it's brand new.
Here's the original owner's posting... This dress was purchased at the BHLDN store in NYC in December 2015 for my summer vintage-inspired wedding. Never worn. Professionally dry-cleaned. Minor alterations: hemmed (I'm 5'8") and straps shortened slightly.