Julia Roberts' beauty secret is a happy expression and a favourite scent. (Picture: CHRIS PIZZELLO, AP)

The 50-year-old actress - who recently shot her second fragrance campaign for Lancôme's La vie est Belle perfume - insists a beauty regime doesn't need to involve much more than a happy expression and a favourite scent.

She told People magazine: "I think as long as everybody smells good and has a smile on their face, that's a beauty regime."

The perfume is the second best selling in the US, and the publication were treated to a sneak preview of the newest campaign, featuring the 'Notting Hill' star's iconic smile.

The series of photos shot by photographer Alexi Lubomirski, show Julia - who has been a face of the brand since 2010 - dressed in a thigh length, long sleeved, white dress, walking through a crowded street while it rains. 

Another is seen through the lens of a camera and shows of the 'Pretty Woman' actress' signature grin, while men in suits pose behind her. 

Meanwhile, despite being one of the biggest movie stars in the world, Julia recently claimed people never recognise her in public - or they think she's a lookalike.

She said: "I don't attract that energy. I get more of, 'Psst, I have to tell you something. People tell me my daughter looks just like you.' Or my favourite, 'You look just like Julia Roberts!' 'Mm-hmm'. 'Are you Julia Roberts?' 'Yes'. 'No you're not.' "

Julia insists she's never been particularly competitive or ambitious and doesn't feel upset if she misses out on work.

She said: "In a business where people can be very competitive and ambitious, I had a strange lack of those emotions.

"When I didn't get a job, I'd think, 'Of course! I would have picked her too. I really believed it all had a purpose."