中でも彼のお気に入りは、母親のお腹にいる時、双子だ ったという少女。
To my surprise, what this sentence says may well affect the meaning of the ending of the book.
So, am I correct that this sentence
does not say anything about the other twin, only that 少女 was a twin while in the womb?
Unless this is a perfectly normal idiom or tactful way to say it, it seems to me like the author has gone out of his way to construct that sentence to
avoid actually saying that the other twin died at birth, although it wouldn't be an unreasonable conclusion to assume that she did, since it only specifies being a twin before birth. (I think once a twin, always a twin, even if your twin was never born, but...)
It just seems to be an odd way to say it unless there's a reason, but I certainly can't judge that, which is why I'm asking.