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1.
Siblings born in the same year to different mothers.

A pun on Irish twins, Black Irish, and the multigenerational deterioration of African-American families.

NB: You don't have to be Black to have a Black Irish Twin.
The other eighth graders thought Dion and Errol were kidding about being "brothers from another mother," but they mean it literally since they were Black Irish Twins.
by PBMax February 23, 2008