Naomi Watts' red carpet secret is well-fitting underwear.

'The Impossible' actress' stylist Jeanann Williams has spilled the beans on what makes the star look so good, saying she never lets her client attend a high profile event without stomach-controlling and cleavage-enhancing underwear.

She revealed: ''Undergarments, like Spanx, smooth everything out ... Silicone petals for the breasts. We use these all the time.''

Jeanann - who made The Hollywood Reporter's 25 Most Powerful Stylists of 2013 list - also explained she gets each outfit customised to fit Naomi's petite frame so she doesn't look swamped in dresses with long hemlines.

The stylist to the stars told ''You have to customize each look to make it work for your measurements and height.

''When dressing clients for the red carpet I always look at the runway image. If my client is 5'5″ [like Naomi], I know I'll need to take the hem up 4 inches.''

The 44-year-old actress favours a simple and sophisticated look, so Jeanann is conscious of keeping accessories minimal.

She added: ''If the dress is dazzling with jewels then go barely-there on the accessories and let the dress be the focus. Don't overdo it, over-the-top is no good.''