Not strictly kings at the nativity. They were Magi or wise men. I think it's only in the song "We three kings" that they are so called. Otherwise, enjoyable grid!

The Flora group is *really* hard. You need to know the specialized subject matter (which I do) but also recognize it when all four are presented as synonyms. Kudos to anyone who got it legitimately.

Very clever and well constructed.

good one..got the categories but ran out of time..:)

The Gilbert and Sullivan was probably a step too far removed from the source. And "three kings" is, as has been pointed out, not in any way accurate. There may have been three, they may have been kings, but nothing says so at source. Whether that account belongs at the Nativity per se is yet another question.