Brian Austin Green Says Raising Gay Son Felt Like 'Unknown' Territory

Brian Austin Green says raising his gay son felt like he was navigating uncharted waters ... but he's making it clear he's got no issues with anyone's sexuality, and he's calling out anyone who feels otherwise.

The former "Beverly Hills, 90210" star opened up about raising his now 21-year-old son, Kassius, on Lance Bass' podcast, "Frosted Tips"' ... saying the situation was all new to him, but it was a challenge he welcomed with open arms.

Lance couldn't help but compliment the actor, claiming it's gotta be a blessing to have Brian as a dad, especially growing up gay.

Brian said there really aren't a lot of differences between gay and straight kids, and it bugs him when other people say they do have a big problem with gay people.

Brian's adamant that someone's preference when it comes to partners isn't a big deal -- a revelation he's, in part, attributing to his relationship with Kassius ... and he says he's been trying to make others see it the same way as him.