Answer:
After the ceremony had concluded
Explanation:
In the sentence, there are two clauses: a subordinate or dependent clause (After the ceremony had concluded) and an insubordinate or independent clause (the prom queen cried tears of joy),
The first one is a subordinate clause because it does not express a complete thought by its own, and therefore, it needs to be with another clause in order to make sense. The second one is an insubordinate clause because it has a full meaning on its own: if you were to remove the first clause from the sentence, the insubordinate clause would still make sense.
Furthermore, After the ceremony had concluded is not only a subordinate clause but it is also an adverb clause because it modifies the action of the second clause by adding information of WHEN the prom queen cried tears of joy.
