Xur is an amalgamation of dead cells(from multiple worlds) that are controlled by the nine's will.
Not sure that could really be his "brother".
English
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Where TF u see that at
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He told me himself. [quote] "I do not entirely control my movements." "Some of the cells in this body began on this world, how strange to return." "I feel a great many consciousnesses impinging on mine, and all of them so small and lonely." "We came up from the dust, and burrowed into flesh for warmth, and became... something new."[/quote]