Ashvatthaman was destined to become the slayer of Dhristadyumna the son of Yajnasena, even as this latter was ordained to be the slayer of Drona.
धृष्टद्युम्नस्य यो मृत्युः सृष्टस्तेन महात्मना। यथा द्रोणस्य पाञ्चाल्यो यज्ञसेनसुतोऽभवत्॥