"When a casual date horse riding down the beach turns into the best day of your life! I can't wait to grow old with you @richiemounga," she said.
World Cup-winning All Black Colin Slade was among the first to congratulate Mo'unga, simply writing, "Congrats brother!"
Mo'unga has come off a stellar year of Super Rugby, claiming the title with the Crusaders and igniting a debate whether he should start for the All Blacks ahead of Beauden Barrett.