Board Thread:General Discussion/@comment-26443838-20150621235438/@comment-24674051-20150623142729

We'll see the black knights in flashback, but not in Storybrooke or the present. A good number were killed by David in the mad dash for the wardrobe. and the ones that did survive may have been personally killed by Regina for failing her (even though they mortally wounded David, he succeeded in getting Emma to the Portal). Regina does not tolerate failure.

Also, any black knights that are remaining were under the same curse, and didn't remember who they were. Regina would likely have punished them for their failures by giving them menial positions. And once they got their memories back, they realized they were free from Regina and just stayed hidden (for fear of her wrath).

It would be kinda interesting if one of the remaining knights showed up, and Regina is like "where have you been hiding?". But unless the storyline needs a black knight to return, I doubt we'll see that.