Hollywood star Russell Crowe has given Bindi Irwin a dazzling $25,000 Rolex watch as she celebrates her birthday engagement to boyfriend Chandler Powell.

Bindi, daughter of the late Crocodile Hunter, Steve Irwin, shared a photo of the solid gold and diamond encrusted watch on Twitter earlier this week. She accompanied the post with a touching message, telling Crowe she had been left "utterly speechless" by his heart-warming gesture which she would "treasure forever".

Crowe – a close family friend – today described Bindi's engagement as "fantastic news" in reply to her announcement that Powell had proposed on her 21st birthday at her family-owned Australia Zoo.

The Gladiator star followed up with another post, comparing Bindi to the expensive watch, writing: "Solid gold. Just Like you. Just like you, It sparkles with real diamonds in its heart. Happy 21st Birthday Bindi."

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Bindi's mum Terri also chimed in to thank Crowe for honouring her daughter on her birthday "and for honouring your friendship with Steve".

Yesterday Bindi and Chandler looked every bit the happy couple as they posed for photos together, with Bindi blowing out the candles on a bumblebee cake.

- Additional reporting by news.com.au