Q:

Trouble understanding why this sentence went to Dative

Here is a quote from Siddhartha from which I am having a little trouble understanding the declension of the article in bold:
"Im Schatten des Hauses, in der Sonne des Flußufers bei den Booten, im Schatten des Salwaldes, im Schatten des Feigenbaumes wuchs Siddahartha auf, der schöne Sohn des Brahmanen, der junge Falke, zusammen mit Govinda, seinem Freunde, dem Brahmanensohn".
I'm looking for an explanation on why dem Brahmanensohn is Dative here, couldn't understand it for myself.
Am I right in assuming the translation for this last part is as follows:
"...the beautiful son of the Brahmins, the young Falcon, together with Govinda, girlfriend of his, the son of the Brahmins."?
It feels that should be nominative but I'm just beginning with grammar so there is probably something basic I'm missing here. 

A:

that part simplifies to

... zusammen mit dem Brahmanensohn ...

(Govinda, and seinem Freunde is simply a list of additional denominations for the same person)
And mit is a preposition that takes the dative.

A:

mit Govinda, seinem Freunde, dem Brahmanensohn

mit requires Dativ case. Govinda, seinem Freunde, dem Brahmanensohn are all in Dativ.
seinem Freunde is easily recognizable as an apposition. Somewhat surprisingly this sentence has a second one with dem Brahmanensohn. That's fairly uncommon in ordinary German. You find it relatively often in religious texts
(e.g., Dem Messias, dem Gesandten Gottes, dem Erlöser, dem Gottessohn jubelten sie zu.). Hesse adopted this style conscientiously, when he wrote Siddharta.

