II Samuel 3:3 Commentary: Rashi

His second [son] was Kilov. [But] in another place¹Divrei Hayomim I, 3,1. [Scriptures] calls him, "and his second [son] was Doniel".²i.e., refers to the second son of Dovid not as Kilov but as Doniel, his true name. So why is his called [here] by the name of Kilov? Rebbe Yitzchok said [to answer this question] : Because the generation's cynics were saying that Avigail was pregnant from Novol,³That Doniel was the son of Novol and not Dovid. [consequently Hashem caused] his facial features to change and resemble his father.⁴His resemblance to Dovid earned him the name of כִלְאָב a play on כּוּלוֹ אָב, “completely his father.” And our Rabbis said⁵Berochos 4a. that [this name of Kilov was due to the fact that] he embarrassed Mephiboshes through Halacha.⁶Doniel’s superior knowledge became evident during the course of his halachic debates with Mipiboshes. According to this Derosho, the letters כל of כִלְאָב stand for מַכְלׅים.

"It was on account of the scoffers of the generation, who said, 'Avigayil (Kilav's mom) was pregnant from Naval (her previous husband),' and so [G-d] changed his appearance and he resembled his father (David)." And our Rabbis said, "Because he embarassed Mephiboshet in law study (Berakhot 4a)"