Here it says that that Achazyahu was 22 when he became king. In Divrei ha'Yamim II, 22:2 it says that he was 42 then! The latter verse is difficult, for his father Yehoram lived only 40 years (32 before he became king, and eight years of kingship - 8:17)!
Rashi (9:29) and Radak, citing Seder Olam 17: Since Asa married his son Yehoshafat to Amri's daughter 1 , it was decreed that Malchus Beis David perish with Beis Achav; Divrei ha'Yamim II, 22:7 says that Hashem arranged that Achazyahu fall with Yehoram 2 . The 42 years are counted from the time of the decree 3 . Yehoshafat married her in the 31st year of Asa's reign, for it says "Amri became king in the 31st year of Asa" (Melachim I, 16:23). He became king six 4 years before this over half of Yisrael. In year 31, he reigned over all of Yisrael. He married his daughter to Asa's son and was elevated, and they killed Tivni (who was competing with Amri to become king from when Zimri died). From Asa's 31st year until Achazyahu Melech Yehudah died 5 was 42 years. Radak - there were nine of Asa, 25 of Yehoshafat, and eight of Yehoram 6 .
Radak: Yehoram lived more than 40 years. The verse counts only eight years that he ruled strongly, but not from when he fell to the Aravim and also fell sick (Divrei ha'Yamim II, 21:16-20). He lived another 20 years without Chemdah 7 . When he fell sick, they made Achazyahu king in his father's lifetime at the age of 22, like it says here. "He ruled one year in Yerushalayim" after his father died. He was 42 when his father died 8 , and they declared him king again (Divrei ha'Yamim II, 22:2 refers to that).
Malbim (Divrei ha'Yamim II, 22:2): When Yehoram ben Yehoshafat fell ill, his son Achazyahu became king, in the 11th year of Yehoram ben Achav. The next year his father died, and he became king absolutely. "Ben Arba'im" there refers to the end of verse 1 (Yehoram was 40 when Achazyahu first ruled); "u'Shetayim Shanah Achazyahu b'Malcho" means that he ruled for two years (including in his father's lifetime), "and one year he ruled in Yerushalayim" alone. I explained (Divrei ha'Yamim I, 8:31), like the Rashbam (Bereishis 36:12), that the first 9 word of a verse can apply to the previous verse.
Rashi: No verse says so! Perhaps "va'Yischaten l'Achav" (Divrei ha'Yamim II, 18:1) means that Yehoshafat married Achav's sister.
Radak: Yehu killed both of them), and Asalyah killed all seed of the royal family [except for Yo'ash; his mother hid him from Asalyah - PF].
Malbim: I.e. it was decreed that Amri's kingship would last only 42 years, and all remembrance of he and his seed would be wiped out. Achazyahu his grandson (via Amri's daughter) became king that year. Therefore he was killed with Beis Achav, to fulfill "v'Hichrati l'Veis Achav Mashtin b'Kir" (Melachim I, 21:21).
Texts of Radak that say '42 years before' are mistaken. Asa ruled for a total of 42 years, and Achav became king in his 38th year, when Amri died 12 (or six) years later (Melachim I, 16:23, 28-29)! (PF)
Why didn't they count 42 years until Achazyahu became king, like Divrei ha'Yamim II, 22:2 and 'Rashi' there say? Radak's calculation omits the one year that Achazyahu reigned! He must say that some years in this calculation were partial years. (PF)
Radak: All of this is far from the simple meaning. What I explained is correct (refer to 8:26:1:2).
We fixed the text to say 'v'Halach' in place of 'v'Malach', like Radak wrote in Divrei ha'Yamim. There (verse 20), it says that Yehoram was "b'Lo Chemdah" i.e. without satisfaction of fulfilling his desire (Metzudas David there).
Malbim: This is difficult. Achazyahu died together with Yehoram ben Achav, who ruled only 12 years. How can it be that there were 20 years in the middle! (Yehoshafat went with Achav to fight in Ramos Gil'ad when Achav died. If there was no gap in Malchus Yisrael, Yehoram ben Achav died 13 years later, after the reigns of his brother Achazyahu (one year) and himself (12 years). There are not 20 years for Achazyahu to reign between Yehoshafat's death and Yehoram ben Achav's death! Perhaps Radak explains that there was a gap of years that are not attributed to Achav's son Achazyahu or Yehoram, until he was firmly established to be king. - PF)
Surely, 'last' in our text is a printing mistake. However, Malbim above and the Rashbam said that the word can apply to both verses. Here Malbim explains that "Ben Arba'im" applies only to the previous verse, i.e. Achazyahu was only 22 when he became king! If so, (a) Ben Arba'im should have been written in the previous verse; (b) It should say 'u'Shtei' (and not "u'Shetayim", since it is not connected to Arba'im). A support for Malbim is the Ta'am of Arba'im (Pashta); it implies that it is not connected to the following word.
Here it says that that Achazyahu's mother Asalyah was Bas Amri. Verse 16 said that the wife of Achazyahu's father Yehoram was Bas Achav!
Radak: Really, she was bas Achav. It says Bas Amri, for grandchildren are like children. Similarly, "va'Tavonah El Re'uel Avihen" (Shemos 2:18) - Re'uel was the father of their father (Yisro). Also "Zerubavel ben She'alti'el" (Chagai 1:1) - really, he was Ben Pu'ah, who was Ben She'alti'el. There are many verses like this.
Malbim: She is called Bas Amri, and verse 27 says that he went in the way of Beis Achav, to teach why he perished with them (refer to 8:26:1:1**).
