One of the NBA's hottest hunks is officially off the market -- with Golden State Warriors star Kelly Oubre, Jr. popping the question to his GF, Shylyn ... and she said YES!!!

The 24-year-old forward announced the big news via Instagram just minutes ago ... sharing emotional footage of the proposal at a private and romantic location.

Oubre and the model first went public earlier this year ... and have been inseparable ever since.