Twins rule. Frey isn't the only god out there with a twin sister. And it's a good thing, too: having a twin isn't always easy, even when she's as cool as Freyja. Sometimes it helps to vent to other gods who are in the same boat.
Apollo is one of the most popular Greek gods and the god of music. Back in ancient Greece he was a total rock star. His twin sister, Artemis, is the goddess of the hunt and the forest. They ran into some trouble even before they were born: you can see the case file here. Eventually, though, their mom, Leto, gave birth to them on the floating island of Delos where Apollo and Artemis spent the first days of their life together.
Xochipilli is the Aztec god of art, music, and games. We know Frey is the twin brother of the Norse goddess of beauty (Freyja) and get this: Xochipilli is the twin brother of the Aztec goddess of beauty, Xochiquetzal. MFEO.