The class of orthogonal relay channels with state in which the source and the relay are connected through a channel that depends on a state sequence is considered. It is assumed that the state sequence is fully known at the destination while it is not known at the source or the relay. The source and the relay are connected to the destination through orthogonal channels. The capacity of this class of relay channels is characterized and it is shown to be achieved by the partial decode-compress-and-forward (pDCF) scheme. To the best of our knowledge, this is the first single relay channel model for which the capacity is achieved by pDCF, while partial decode-and-forward (pDF) and compress-and-forward (CF) schemes are suboptimal in general.