@MojangSupport can't join a realm. Friend can't join either and it's his realm. Are the servers down?
I'm really sorry you're having trouble! It sounds like a possible temporary issue that we're looking into, but if it's still happening later on, I would recommend looking into our Realms article here for further help: https://help.minecraft.net/hc/en-us/articles/360034754132-Minecraft-Realms-connection-issues …. Thanks! ^AS