Green’s Dictionary of Slang

an excl. of surprise.

1901		Boy’s Own Paper 27 July 674: ‘Just fancy!’ he said to himself.
1905		H. Green Actors’ Boarding House (1906) 203: Fancy! Really, her father would want to kill me.
1941		K. Tennant Battlers 201: Fancy that poor woman and the boy coming to find the father! Fancy, now!
1997–2000		College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 Aw Fancy...What the hell? (phrase) What?? Damn! [Oxnard High School, Oxnard, CA].