Psalm 69:8

During my Bible reading, this verse (particularly the second half) piqued my curiosity.  What exactly did it mean by, “an alien unto my mother’s children”?  Liberty Bible Commentary says, “As the preference of David over his elder brethren aroused their jealousy (1 Sam 16:6-13), so too the Son of David was alien to the younger children of Mary during His earthly ministry (Jn 7:5); but they joined His followers after His resurrection (Acts 1:14).