From Longman Dictionary of Contemporary Englishbe the apple of somebody’s eyebe the apple of somebody’s eyeLOVEto be loved very much by someone Ben was always the apple of his father’s eye. → apple
Examples from the Corpus
be the apple of somebody’s eye• Ben was always the apple of his father's eye.• He was the apple of her eye, the salt of her earth, the source of her strength - her everything.• Lucy's son was the apple of her eye, work her raisond'être. 