John Gill Commentary 2 Samuel 13:1

"And it came to pass after this, that Absalom the son of David had a fair sister, whose name was Tamar; and Amnon the son of David loved her." — 2 Samuel 13:1 (ASV)

And it came to pass after this
After the sin of David with Bathsheba, his repentance for it, and pardon of it, and the birth of Solomon as a token of reconciliation; yet after all this the divine threatenings must take place; they had begun already in the death of the child begotten in adultery, and others here follow:

that Absalom the son of David had a fair sister, whose name [was]
Tamar ;
she was his sister both by father and mother's side; the mother o, f them was Maacah, the daughter of Talmai king of Geshur; she was a very comely person, her name signifies a palm tree:

and Amnon the son of David loved her ;
not in an honourable way, to make her his wife, but in a lustful manner, to make an harlot of her; he was David's eldest son by Ahinoam the Jezreelitess, (2 Samuel 3:2) .