The two food-loving pals, who hosted the Big Feastival event on James' Oxfordshire farm, played bass and drums with the group after agreeing to perform at the last minute.
Cuban Brothers frontman Miguel Mantovani tells the Bbc, "It was unrehearsed. They jumped on stage with us and they can hold their own. They're great guys and it was nice to have them join us."
It's not the first time James and Oliver have played at the festival - they took to the stage last year (12) for the event's debut and performed as The Farm Lovin' Criminals.
This year's festival was headlined by The Feeling and featured sets by Mark Owen and KT Tunstall.