(3x15) Light of the Foundation: Part 2, Episode 3
The Einherjar are terribly sorry for disobeying orders and bringing this alien ship to Sol, but they ask everyone to please stop firing on them. They apologize that they didn't open communications sooner but they weren't sure talking would do any good since everyone opened fire on them immediately. But it's clear now why that was: because of the war that's obviously going on here. Lastly, they ask humanity to also cease fire on the aliens, because there is clearly some enormous miscommunication that has happened. Their ship's AI recognizes the life-forms aboard the alien command ships as Ehrban, the people of Keius Meij, the one who made the immortals immortal thousands of years ago.
Another transmission in an unknown encoding is broadcast immediately afterward, and as the Foundation and the rest of humanity's forces pull back and regroup in light of this information, so too do the alien ships. The Einherjar relay to the Foundation that their new ship's alien AI has established communication with the Ehrban and asked them to stand down as well. Talks between the Foundation and the Ehrban leadership are soon established with the help of that AI's translation services, it having learned human speech from the Einherjar and Ehrban speech because its creators, the Asiron, were created by Keius Meij as well.
In those talks it soon turns out that the human commanders (the Foundation plus Kron and his Horsemen) and the Ehrban both thought the other side was an enemy they have in common, those from whom Keius Meij closed the wormhole from the Sol side to protect humanity, and whom these modern Ehrban have been fighting a second war with for some time: a species called the Berol. With that cleared up, apologies are made from both sides for the misunderstanding, and both sides are fascinated to meet the other at last: the Foundation are fascinated to meet the people of their creator Keius Meij, and the Ehrban are fascinated to meet the near-mythical "adopted children" of Keius, who is as ancient and mysterious a figure to them as he is to the Foundation. But peace at Sol, it turns out, is very short-lived, as the Berol war already raging in other systems held by the Ehrban soon spills out into the Sol system as well.
Next: Light of the Foundation: Part 3, Episode 1