Brandon Blackstock's oldest son, Seth, is breaking our hearts. Seth, of course, is one of the late talent manager's four children, along with his expecting sis Savannah as well as his younger half-siblings River, 11, and Remington, 9, whom Brandon had co-parented with ex Kelly Clarkson. And on Friday night, the 18-year-old took to Instagram to publish a truly crushing memorial for his dad, who died earlier this month after a battle with cancer.