What is the ruling regarding legal accountability (Hudud and sin) if the usurper was ignorant of the prohibition?

Primary text

If the usurper was ignorant of the prohibition due to recent conversion to Islam or being raised in a remote area where such matters are unknown, and he believed intercourse was permissible or thought the slave was his own property, then the Hadd punishment is lifted because Hadd is repelled by apparent doubts (Shubuhāt). He remains liable for the Mahr and the compensation for the loss of virginity.