Grapefruit and Sugar Rubbed Pork Tenderloin

Name: Grapefruit-and-Sugar-Rubbed Pork Tenderloin
Ingredients: 1 cup packed dark brown sugar; 1 tbsp. smoked sweet paprika; 1⁄2 tsp. ground cumin; 1⁄2 tsp. ground fennel; 1⁄4 tsp. cayenne; 5 cloves garlic, peeled; 2 grapefruit, 1 pink or red grapefruit and 1 white, zested and supremed; Kosher salt and freshly ground black pepper, to taste; 1 (1 1/2-lb.) pork tenderloin