Whisk together the ketchup, Dijon mustard, soy sauce, olive oil, apple cider vinegar, thyme and black pepper in a bowl. Place the pork tenderloin in a zipper sealable plastic bag. Pour the marinade over the pork and massage the marinade into the meat. Marinate the pork in the refrigerator for at least four hours to overnight.

Remove the pork tenderloin from the marinade. Pour the marinade into a saucepan and whisk in the brown sugar. Bring the mixture to a boil, lower the heat and simmer for about 10 minutes until the sauce thickens.

Heat an outdoor grill or grill pan to medium-high heat. Grill the pork for 15 minutes, rotating a few times during the cooking process. Baste the meat with some of the BBQ sauce and grill for an additional 5 minutes, until the pork reaches the internal temperature of 145°F with an instant read thermometer.

Remove the pork from the grill and tent with foil. Let the pork rest for 10 minutes before carving. Slice the meat into thick slices, slicing on an angle across the grain of the tenderloin. Transfer to serving platter and pour the remaining sauce over top. Serve with rice, potato salad, green salad or any of your favorite grilled side dishes OR make quick BBQ pork sandwiches on Kaiser rolls with coleslaw.