“Pawn Stars” creator and lead star Rick Harrison is grieving the sudden loss of his son Adam, who recently died of an overdose at age 39. The reality star, 58, shared a photo of himself and Adam on Instagram late Friday night. “You will always be in my heart! I love you Adam,” Harrison wrote. Harrison’s representative confirmed Adam’s cause of death with the Las Vegas Review-Journal on Friday. Sources previously told TMZ the family only learned of Adam’s death earlier that day, though it’s unclear when exactly he died. The specific circumstances surrounding his death are also unknown. What sub…