Two Routes:
1) Stealth. Kill your enemies in secret (including the prince).
2) In Their Face: Slaughter him mercilessly in public. Play with him first, let him get his magic off, and show that it's useless. Drive him into the ground. Hopefully he starts begging for his life. But whether he does or not, kill him gruesomely and mercilessly. Then turn to watching nobles and ask, "Who's next?" After that, start tracking down those who are plotting against you in secret and kill them off too.