In the upcoming film Diana, Watts is playing the world's most iconic woman - the 'people's princess'.

Watts might be an A-list international star, but she is still just another working mum juggling a career and a young family.

Earning more than $5 million a movie, and starring opposite some of Hollywood's biggest names, Watts has come a long way from her acting gigs.

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She once appeared in a TV ad, and did Home and Away as well - though she's unashamed of her beginnings, unlike former Home and Away star Melissa George who last week lashed out at reporters always bringing up her first acting job.

"Why not (embrace it)," she asked. "I mean you know, work begets work, that's always been my philosophy. My goodness, I've had to come from doing things that certainly I'm not that proud of, but you know, it all gets you to the next place."

And all those jobs have led her to the role of a lifetime - playing Princess Diana.

"It's nerve-wrecking every time I begin to speak about it," Watts said of her role. "You fear the judgement that comes with the comparisons - 'is she tall enough, is her nose right, is her hair right'. The whole preparation for this movie was very intense and much more extensive than I've ever done, just simply because she was the most famous woman of our time."

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And just like Princess Diana, who supported Sydney's St Vincents Hospital's Vincent Chang Institute just ten months before she died, Watts is in Australia backing the hospital's Kinghorn Cancer Centre's Look Good Fee Better charity.

She's promoting Pantene's Beautiful Lengths program as their global ambassador - a campaign to inspire women to grow, cut and donate their hair to be made into wigs for cancer patients.

More stories from reporter Laura Sparkes

• Look Good Feel Better - www.lgfb.org.au
• Pantene Beautiful Lengths - www.beautifullengths.com.au

This reporter is on Twitter at @LauraSparkes7