"Love & Hip Hop: Atlanta" alum D. Smith says he's detransitioning after living publicly as a transgender woman for 12 years ... and will now present as a man and use he/him pronouns.

The Grammy-nominated producer announced the change Thursday on Instagram, saying the decision has been taking shape over the past several months.

Smith says those years were not a mistake and aren't something he's trying to erase ... writing, "Living my life as a woman for 12 years showed me the man that I wanted to become."

He also stressed his love and respect for the transgender community remain unchanged ... and says everyone deserves the freedom to become themselves.

Smith added there's much more to his journey than he could fit into one statement, and plans to share the full story when the time is right.

He publicly came out as transgender in 2014 and joined "Love & Hip Hop: Atlanta" two years later ... becoming the show's first openly transgender cast member.

The two-time Grammy nominee has worked on music with artists including Katy Perry, Lil Wayne, and CeeLo Green.