I found my child watching pornography

My son is 9 years old and has always been very demanding but a great child in every sense. In the past weeks he told me he had to do his homework and I found him watching lesbian pornography. I don’t want to control but to guide him. I didn’t reprehend him but told I was very upset because I trusted and he lied to me, besides, pornography is totally inappropriate and could harm him. How can I support in the best way possible??? Any ideas???? Please help