Well, it wasn't exactly a revelation to me, because I'd known it for a while, but it was to an uncle of Cabbage and me.
Uncle was visiting us, and Grandma, Uncle, and I were making dinner. Meanwhile, Grandpa, Dad, and Cabbage were having a discussion about Bach, and Mom was in another room. Cabbage started adding to the discussion, and Uncle whipped around, looking confused. You see, Cabbage and Mom sound so alike that even our mom's own brother mistook their voices. It took me a solid two years (from 16 - 18) to be able to tell them apart, and I live with them both for at least part of the year.
Cabbage still vehemently denies the similarity, but Uncle's reaction proves my point.