Orgin of phrase "Oh my giddy aunt"

I recently heard the phrase "Oh my giddy Aunt" used in
a movie, and wonder where it originated? I beleive the
movie was "A Knights Tale".

My "giddy aunt" is an expression used to denote surprise. The "giddy" in this instance is probably unrelated to a sense of spinning around but rather to an alternative meaning of the word indicating "impulsive" or "scatterbrained" (Old English gydig meant "mad, frenzied, possessed by God"). The expression is much older than the movies!