Ahithophel the Gilonite

• Wikipedia: Ahitophel & אחיתופל.

Ahitophel was King David's trusted advisor, and grandfather of Bathsheba.

Why did Ahithophel betray David after so many years faithful service?

Ahithophel had been King David’s faithful counsellor for many decades, giving David the benefit of his great wisdom which was so brilliant, it was as if a man had inquired the Word of God (2 Samuel 16:23).
When David learned his trusted friend had betrayed him, he was so afraid, he prayed, “O Lord I pray You, turn Ahithophel’s counsel into foolishness” (2 Samuel 15:31).