Read this and answer the question

A week after the implementation of the no-fly zone, NATO announced that it would be enforced. On 30 April a NATO airstrike killed Gaddafi's sixth son and three of his grandsons in Tripoli, though Gaddafi and his wife were unharmed. Western officials remained divided over whether Gaddafi was a legitimate military target under the U.N. Security Council resolution. U.S. Secretary of Defense Robert Gates said that NATO was "not targeting Gaddafi specifically" but that his command-and-control facilities were legitimate targetsincluding a facility inside his sprawling Tripoli compound that was hit with airstrikes on 25 April.

What organization killed Gaddafi's grandsons?
NATO