1 Kings 2:11

And the days that David reigned over Israel, forty years: in Hebron he reigned seven years, and in Jerusalem he reigned thirty and three years.

The son of thirty years was David in his reigning, and he reigned forty years.

And David son of Jesse reigned over all Israel.

Treasury of Scripture Knowledge

And the days that David reigned over Israel were forty years: seven years reigned he in Hebron, and thirty and three years reigned he in Jerusalem.

The son of thirty years was David in his reigning, and he reigned forty years.

And David son of Jesse reigned over all Israel.