born on the wrong side of the blanket

born on the wrong side of the blanket

Rur. [of a child] illegitimate. All his life, Edward felt that people looked down on him because he was born on the wrong side of the blanket. Just between you and me, I suspect Mrs. Potter's oldest child was born on the wrong side of the blanket.
See also: blanket, born, of, on, side, wrong