The Pulpit Commentary - 2 Samuel 13:1
EXPOSITION After this. This phrase, as we have seen on 2 Samuel 10:1 , has little chronological force, but the date of the sad event which formed the second stage in David's punishment can be settled with considerable certainty. Tamar was the daughter of Maacah, a princess of Geshur, and David's marriage with her, while still at Hebron, is mentioned as a proof of his growing power, and consequently some time must have elapsed after his appointment as king before this alliance took... read more
Adam Clarke's Commentary on the Bible - 2 Samuel 13:21
But when King David heard - To this verse the Septuagint add the following words: Και ουκ ελυπησε το πνευμα Αμνων του υἱου αυτου, ὁτι ηγαπα αυτον, ὁτι πρωτοτοκος αυτου ην ; "But he would not grieve the soul of Amnon his son, for he loved him, because he was his first-born." The same addition is found in the Vulgate and in Josephus, and it is possible that this once made a part of the Hebrew text. read more