under someone's spell
Fascinated or influenced by someone, as in I think he has our daughter under his spell. This idiom derives from the literal meaning of spell, “a word or formula that has magical power.” [Mid-1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.