Yuusha Party no Nakama ni Maou ga Mazatterurashii.

Keep your friends close and the demon king closer! Kyle was reincarnated into a fantastical world as a member of the hero’s party. Over the course of their journey, he’s forged unbreakable bonds with his crew—Noelle the high priestess, Dal the thief, Tiger the beastfolk, Sasha the mage, and Eclair the hero. Their expedition seems to be going well, when suddenly, a goddess appears to tell Kyle an earth-shattering secret: One of his dear friends is actually the Demon King in disguise. Can he figure out the identity of their greatest foe before it’s too late?! Source: Yen Press