Bryan Singer & Gary Goddard -- New Accuser Sues ... It Started When I Was 14

Bryan Singer and Gary Goddard have just been sued by another man who claims the showbiz honchos sexually assaulted him as a boy ... a campaign of abuse he says started when he was just 14.

The lawsuit was filed today on behalf of a John Doe -- now 25 -- who claims Goddard established an online relationship with him back in 2003, and it quickly escalated into nude video chatting. The accuser alleges Goddard masturbated during these video chat sessions.

When he was 16, the accuser alleges Goddard invited him to London where they engaged in anal intercourse. The accuser claims Singer got involved roughly a year later in 2006 following the London premiere after party for "Superman Returns."

He claims Singer and Goddard plied him with alcohol during the party and brought him back to a hotel room, where a muscular man forced him into submitting to Singer and Goddard's sexual advances.

The accuser claims he refused to have sex with Singer, so Singer asked him to sit on his chest and ejaculate instead. Singer has adamantly denied the allegations.

The lawsuit was announced during a news conference Monday by the accuser's attorney Jeff Herman, who also showed blacked-out photos of his client hanging out with Goddard and Singer on the red carpet. The alleged victim was not present during the news conference.

Herman says the accuser was inspired to come forward by his other client -- 31-year-old Michael Egan -- who is also suing Singer and Goddard (as well as others) with similar allegations of underage sex abuse.