The answer is: Amnon

2 Sam 13:7-14 - Half sister to Amnon, but whole sister to Absalom

The story of Amnon and Tamar is one of the most tragic and startling narratives nestled within the pages of the Old Testament, revealing the personal struggles and intense family dynamics within King David’s household. Tamar, being marked as both a victim and a key character, is actually the daughter of David's wife Maacah. Notably, she and her brother Absalom shared the same mother, giving this story a deep twist when familial loyalties and tragic events collide.

In 2 Samuel 13, this episode doesn't stand alone. It echoes themes of power, control, and the severe consequences of unchecked desires. Amnon’s obsession leads to a depraved act that causes a ripple effect in David’s family. Absalom, enraged by the injustice done to his sister, vows revenge, which inevitably spirals into blood feuds and further tragedy for David's line. Interestingly, the chaos in David's family forced him to confront the breaking points of his own leadership and moral authority—foreshadowing the fate that would ultimately befall his reign.

This story, while grim, offers profound lessons about the dynamics of power, abuse, and family. It imparts knowledge on how the consequences of one person's actions can devastate an entire family tree, hinting at a message around the value of justice, integrity, and the importance of listening to the voices of those who’ve suffered. As Shakespeare might say, "What's done cannot be undone," clearly illustrating the lasting scars left in both individual lives and a broader historical fabric.