monkey's uncle, I'll be/am a

I'll be a monkey's uncle

used to express great surprise. informal
See also: uncle

monkey's uncle, I'll be/am a

An expression of surprise or disbelief. Why that particular animal was chosen is no longer known, and indeed the cliché, which dates from the early 1900s, is heard less often today. Eric V. Lustbader used it in White Ninja (1990): “If this doesn’t turn out to be a suicide, I am a monkey’s uncle.”