When David was really really old, he became sickly and frail. He was cold all the time, so his people decided that what he needed was a beautiful young virgin to tend to him and to sleep naked with him to warm him up. Her name was Abishag.
Adonijah, son of Haggith, decided that since David was so close to dying and he was now the oldest since Absalom was dead, he should start acting like the heir apparent. So he got himself a retinue and followers. Joab and Abithar the priest decided to back his play. However, Zadok and the other mighty men didn’t want any part of it.
One day Adonijah decided to go down to the Serpant’s Stone to make a huge sacrifice and throw a big party in anticipation of his reign, but he didn’t invite Solomon or Nathan or any of the mighty men.
This irked Nathan, so he went to Bathsheba and was all, Do you know that Adonijah has set himself up as king? If you value your life and the life of your son, you’ll do what I say.
So Bathsheba went to David and was all, Why is Adonijah king? I thought you promised me that Solomon would be king after you.
Then Nathan came in and was all, Oh King, Did you make Adonijah your heir? Because he’s throwing a party and everyone is calling him king.
So David declared before the court that Solomon was, in fact, his heir. Then Zadok and Nathan took Solomon down to Gihon and anointed him king. Word was brought to Adonjiah that David had outfitted Solomon as the heir apparent–which really put a damper on the party.