The last word in the book of Revelation is "Amen." which indicates that it might be the prayer of someone.
1. "Amen" at the end of a prayer is an expression of agreement with what was prayed for and means "So be it". However "Amen" has other applications also.
2. When Christ said "Verily, verily" (or "truly, truly"), He actually said "Amen, Amen".
Strong's Concordance
amén: truly
Original Word: ἀμήν
Part of Speech: Hebrew Form (Indclinable)
Transliteration: amén
Phonetic Spelling: (am-ane')
Definition: truly
Usage: verily, truly, amen; at the end of sentences may be paraphrased by: So let it be.
Thayer's Greek Lexicon
STRONGS NT 281: ἀμήν
a.
at the beginning of a discourse, surely, of a truth, truly; so frequent in the discourses of Christ in Matthew, Mark, and Luke
b.
at the close of a sentence; so it is, so be it, may it be fulfilled
So in Revelation 22:20,21 it means "
may it be fulfilled"