The Regina Caeli (“Queen of Heaven”) is a prayer that is closely associated with Easter. We usually recite this prayer instead of the Angelus during the Easter Season, at which time it also serves as the the Marian Antiphon at the end of Compline (Night Prayer). The beautiful musical setting for the Regina Caeli below was composed by Gregor Aichinger (1565-1628), and is performed here by the Zürcher Sing-Akademie.
The prayer Regina Caeli itself is of ancient origin. Our oldest record of it comes from the twelfth century, but the website ourcatholicprayers.com tells us:
According to The Golden Legend, a famous 13th century work about the saints, Pope St. Gregory the Great heard angels singing the first three verses from the Regina Caeli during a procession in the 6th century and was inspired to add the fourth line “Ora pro nobis deum” (“pray for to us to God” in Latin). Although this story is itself considered to be a legend, it is, as Father Herbert Thurston once put it in his book Familiar Prayers, “inseparably associated with the Regina Caeli.”
I have posted the prayer in both English and Latin below (the clip itself has subtitles in Latin and German).