Mary resided in "her own house"[Lk.1:56] in Nazareth in Galilee, possibly with her parents, and during her betrothal — the first stage of a Jewish marriage — the angel Gabriel announced to her that she was to be the mother of the promised Messiah by conceiving him through the Holy Spirit, and she responded, "I am the handmaid of the Lord. Let it be done unto me according to your word." After a number of months, when Joseph was told of her conception in a dream by "an angel of the Lord", he planned to divorce her; but the angel told him to not hesitate to take her as his wife, which Joseph did, thereby formally completing the wedding rites.[Mt 1:18-25]
In his dream, who told Joseph about Mary's conception?
an angel of the Lord