On Sunday she posted a picture showing a small portion the lacy sleeve of her dress in what appears to be a bridal shop.
“I said yes to the dress,” the caption read.
Powell, 22, proposed in July in honor of her 21st birthday.
He tweeted “She said YES!” along with a photo of him and Irwin after he proposed.
“Almost 6 years ago we met at Australia Zoo. I immediately fell head over heels for your kind and thoughtful heart that radiates so much light,” his tweet read. “I love you more than anything in this world and I always will. Forever together sounds perfect.”
“It just so happened that Bindi was giving tours that day,” Powell said. “I’m like, ‘Wow she is amazing.'”
Powell relocated from Florida to Australia to live with the Irwins, who have carried on the work of their late patriarch.
Bindi Irwin was 8 years old in 2006 when her father, crocodile hunter and wildlife conservationist Steve Irwin, was killed by a stingray during a television shoot.