But you was a real nigga
I could sense it in you

from Dr. Dre (Ft. Eminem & Xzibit) – What's the Difference Lyrics on Rap Genius

Meaning

Despite their professional difficulties, Dre recognizes The D.O.C.’s realness (possibly because D.O.C. ghostwrote a bunch of Dre’s lyrics)

Could be a poke at Ice Cube as ‘Real Niggaz’ was the name of the diss N.W.A put out towards Cube after he left.
Cube literally left because of the “business end” of things and as said in the previous line, it can turn your friends against you but D.O.C was a “real nigga” which Dre puts a lot of emphasis on in this line.

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