Oh, my giddy aunt

"Oh, my giddy aunt" was a colloquialism that was often used as an exclamation of surprise.

The Brigadier said this when he found out that Professor Rubeish was missing. (TV: The Time Warrior)

The Second Doctor used the phrase often. He said it to Dastari during an argument in the cellar (TV: The Two Doctors) and said it when surprised by a Kroton. (TV: The Krotons)

Missy said it to Clara while they were on a plane. (TV: Death in Heaven)