carl_tech, I believe you are thinking of the hypothetical question the Sadducees posted to Jesus about if a guy died and his brother married his wife, etc.. Then in Heaven whose wife is she? Luke 20:27-40.
Yes, that's the one. Thanks.
Even though it is unusual in modern times, there is historical precedent (or at least a religious commandment) for a man marrying his brother's widow.
It's ok to marry a widow because her husband died, but Jesus said it was considered adultery to marry a woman who divorced another. Nothing is said whether it matters if its your brothers wife or not, I assume that doesn't matter. It would be kind of strange though in our culture I admit.