Bindi Irwin has announced her engagement to long-time boyfriend Chandler Powell on her 21st birthday.

The daughter of late Crocodile Hunter revealed the upcoming nuptials on Instagram after six years of dating.

“On my birthday I said ‘yes’ and ‘forever’ to the love of my life,” Ms Irwin posted on Wednesday.

“Chandler, close to 6 years ago I fell in love with you and every day since has been a whirlwind of adventure and true happiness.

“I’m so looking forwarding to spending our forever together as your wife. Here’s to a lifetime of friendship, purpose and unconditional love.

“Now let’s get married already!”

Bindi is the eldest child of Steve Irwin who died aged 44 in 2006 while filming on the Great Barrier Reef when a stingray’s barb struck him in the heart.

She met Steve-lookalike Chandler, a wakeboarder from Florida, when he was visiting Australia Zoo.

Chandler also took to Instagram to reveal details of his romantic proposal, declaring “She said YES!”.

“Almost 6 years ago we met at Australia Zoo. I immediately fell head over heels for her kind and thoughtful heart that radiates so much light,” he wrote.

“Proposing in her very favorite place in the zoo, surrounded by animals, seemed like the perfect way to embark on this incredible new chapter in our lives.

“Bee, I love you more than anything in this world and I always will. Happy Birthday.”

Earlier the couple had posed together for Bindi’s official birthday celebrations at the Sunshine Coast-based zoo with mum Terri and brother Robert.

Chandler Powell, Bindi Irwin, Terri Irwin and Robert Irwin at Bindi’s 21st birthday celebration at Australia Zoo. Photo: AAP

Terri Irwin responded with her own social media post, saying her late husband Steve would have been proud while Robert offered a love heart emoji.

Best day ever! Chandler asked and beautiful @BindiIrwin said yes. I am so very happy, and I know Steve would be too. Congratulations!! pic.twitter.com/sN5sFnxZhI

— Terri Irwin (@TerriIrwin) July 24, 2019