What does 2 Samuel 11:21 mean?

'Who killed Abimelech son of Jerubbesheth? Didn’t a woman throw a millstone on him from the wall at Thebez, and he died? Why did you get so close to the wall?'—then say, "Your servant Uriah the Hittite was killed too."' 2 Samuel 11:21 - Modern Text Bible

(Joab tells the messenger to mention Uriah’s death if David questions their strategy, knowing this is what David really wants to hear.)