'Fourth Generation' in the Bible

And Jehovah said to him, Jehu, because you have done well in doing the right in My eyes, and have done to the house of Ahab according to all that was in My heart, your sons of the fourth generation shall sit on the throne of Israel.

This was the Word of Jehovah which He spoke to Jehu, saying, Your sons shall sit on the throne of Israel until the fourth generation. And it was so.