If a person catches up while the Imam is in the Ruku position, he is ordered to join the Imam and his rak’ah is valid even though he did not recite the Fatiha.

Me and a brother join in the Ruku with the Imam from the first rakha. After the salam the brother raised up and added one more rakah. He explained that as he could not recite sura Fateha, it is recommended to repeat that rakha?