Sydneysider Millie announced the split via her Instagram account, telling her followers, "Mark and I have had such an amazing time together and we will forever cherish our special moments, unfortunately at this point in time we have decided we are both going in different directions and have to part ways."
She added, "We still remain very close friends . Thank you everyone for your support and we hope right now you can respect our privacy."
The shock post comes weeks after Millie posted a loved-up snap of her and Mark to Instagram, in celebration of their anniversary.
"6 months (well just over 6 months) of being the luckiest girl in the world," she wrote.
Millie accompanied the message with a quotes, "Don't cry because it's over, smile because it happened."