According to 1 Samuel 15:35, Samuel mourned for Saul, and God regretted that He had made Saul king.
It is hard to understand how God, who does not repent or change His mind (Numbers 23:19, 1 Samuel 15:29), can regret something. In other places, Scripture speaks of God’s regret. For example, Genesis 6:6 says:
Genesis 6:6 (NKJV) And the Lord was sorry that He had made man on the earth, and He was grieved in His heart.
The rebellion, sin, and wickedness that the human race chose grieved the heart of God. God grieves over His fallen creatures.