Albert Barnes Commentary 2 Samuel 13:35

"And Jonadab said unto the king, Behold, the king`s sons are come: as thy servant said, so it is." — 2 Samuel 13:35 (ASV)

The watchman, as was his duty, had sent immediate notice to the king that he saw a crowd approaching (see 2 Kings 9:17–20). Jonadab, who was with the king, was prompt to give the explanation.