Peel and section grapefruit over a serving bowl to catch juice. Measure 1/2 cup grapefruit juice. Reserve remaining juice for another use, if desired. Add grapefruit to bowl. Set aside.
Bring reserved 1/2 cup grapefruit juice, sugar, honey, and 3 mint sprigs to a boil in a saucepan over medium heat; boil 5 minutes. Remove from heat, and cool completely. Remove and discard mint.
Pour mint syrup over fruit in bowl. Cover and chill 8 hours. Garnish, if desired.
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