In the beginning of the Lokasenna, Bragi denies Loki a seat with the gods. However, Loki reminds Odin that the two of them had their "blood mixed", and that Odin had promised that neither of them would drink with the gods unless both of them were welcomed. Odin is then left with little choice but to order Vidar to find a seat for Loki:
8. "A place and a seat | will the gods prepare
No more in their midst for thee;
For the gods know well | what men they wish
To find at their mighty feasts."
9. "Remember, Othin, | in olden days
That we both our blood have mixed;
Then didst thou promise | no ale to pour,
Unless it were brought for us both."
10. "Stand forth then, Vithar, | and let the wolf's father
Find a seat at our feast;
Lest evil should Loki | speak aloud
Here within Ægir's hall."
Is there a story that explains how Odin and Loki came to be blood brothers?