Noun
jewel in the crown (plural jewels in the crown)
(idiomatic) The most valuable or important thing or person among others of its kind.
The goalkeeper is the jewel in the crown and getting at him should be almost impossible. It's the biggest sin in football to make him do any work. George Graham
He was the undisputed jewel in the crown of Indian music; one who will not be born in the next few centuries. He gave a new meaning to shehnai. Bismillah Khan
I felt privileged to be a facet of such a jewel in the crown of American cinema. Tatum O'Neal