Kate Middleton was the middle-class girl who made becoming a princess look easy -- but bringing up a royal baby will bring fresh challenges for Britain's glamorous future queen.

Since her fairytale marriage to Prince William in 2011, 31-year-old Catherine, Duchess of Cambridge, as she is now formally known, has hardly put a foot wrong.

Reportedly once nicknamed "Little Miss Perfect", the glossy brunette has breathed new life into the monarchy, drawing comparisons with William's late mother Princess Diana.

And as the first "commoner" to marry a future king since 1660, she has helped bring the royals closer to ordinary Britons.

Kate's great-great-grandfather was a humble coal miner, although hers is no rags-to-riches story -- her parents are self-made millionaires from a party supplies business.

Michael and Carole Middleton met at British Airways, she as an air hostess and he as a flight dispatcher. Catherine, their first child, was born in the town of Reading, west of London, in 1982.

The family lived in Jordan when Kate was a toddler, before returning to Britain and setting up their company Party Pieces in 1987.

Kate was sent to the expensive Marlborough College boarding school, where she mingled in the same aristocratic circles as William.

But it was not until 2001, studying history of art at St Andrews University in Scotland, that she met her husband-to-be.

"She was known as Beautiful Kate almost from day one," recalled former student Helen McArdle in a television documentary.

Known at school for being hard-working and sporty, Kate kept up her whiter-than-white image at university -- with a couple of exceptions.

There was the student fashion show where she wore a transparent dress -- the moment, legend has it, that she caught the prince's eye. McArdle also remembers seeing the future duchess "paralytically drunk" on one occasion.

After university, while William began his military training, Kate worked for Party Pieces and took a part-time job as a fashion house buyer.

Alone in London, she was hounded by photographers in a grim reminder of the media's hunger for Diana, who died in a car crash in Paris in 1997, pursued by paparazzi.

Nicknamed "Waity Katie" by British tabloids and reportedly mocked by William's circle, who would whisper "doors to manual" when she entered a room because of her mother's old job as a stewardess, it was a difficult time.

It was made worse when William dumped her in 2007.

Many jilted girlfriends would have got revenge by selling their story, but Kate maintained a dignified silence during the brief split.

"At the time I wasn't very happy about it," she later said of the break-up. "But it made me a stronger person."

Since then she has won praise for her poise in the intimidating world of the royals.

Her Alexander McQueen wedding gown installed her as a fashion icon, while her mix of designer labels and high street bargains has made her a fixture on "best dressed" lists.

Echoes of Diana, meanwhile, are never far away.

In September the royals sued over photographs of Kate sunbathing topless in France, raising fears Kate could face the same intrusion.

And as with Diana, there was constant speculation about when she would produce an heir.

The announcement came in December when the duchess was hospitalised with morning sickness.

The suicide days later of a nurse at the hospital who fell victim to a hoax call by two Australian DJs wanting news of Kate cast a pall over what should have been a happy time.

The duchess has since returned to work, flashing her megawatt smile and promoting her various charities.

But while hugely popular she remains, in many ways, a mystery.

Her reserve has fed claims that she is boring -- novelist Hilary Mantel described her as a "shop-window mannequin" with a plastic smile.

It is rare to hear her speak -- and if she has a "naughty sense of humour", as William says, it is kept well hidden from the public.

Like any new mother, she faces exhausting months ahead.

The difference is that Kate's child will one day be monarch -- making her one of the most scrutinised mothers on the planet.