Profile: Kate, Duchess of Cambridge
The Duchess of Cambridge has moved from a comparatively ordinary existence to a prominent role in the Royal Family since she started going out with Prince William in 2001.
The couple met while Catherine Middleton was studying art history at St Andrews University, in Fife - where they shared accommodation for four years.
Their wedding at Westminster Abbey in April 2011 was watched on television by millions of people around the world.
And the announcement in December that the couple were expecting their first child has thrust the duchess into the media spotlight like never before.
Catherine Middleton was born on 9 January 1982.Popular and talented
She grew up in Bucklebury, in Berkshire, where her parents, Michael and Carole Middleton, run a mail-order business selling toys and games for children's parties from a converted barn close to their home.
The eldest of three children, she was educated at the exclusive Marlborough College in Wiltshire, where she was described as level-headed, popular and talented, and captained the school hockey team.
Her sister Pippa, 29, has raised her profile since she was maid of honour at the royal wedding. She has written a party-planning book and is now contributing editor for the magazine Vanity Fair.
Her brother, James, 26, has founded a baking company.
After they met at St Andrews, Catherine and William's relationship apparently flourished during weekends together on the Queen's Balmoral estate.
For a while, at least, they were guaranteed some privacy, following an agreement worked out between the palace and press while William was a student.
But the media silence did not last, and Catherine was first brought to the public's attention after several tabloids pictured her beside Prince William and Prince Charles at the Swiss ski resort of Klosters in 2005.
The photographs appeared despite efforts by aides to keep the holiday private.
Newspaper interest grew when Catherine graduated, moved to London and started work as an accessory buyer for high street clothes shop Jigsaw.
In October 2005, after the publication of a photo which showed her looking out of a window on a London bus, her lawyers wrote to newspaper and magazine editors asking them to respect her privacy.
They claimed photographers had followed Catherine almost every day and night since she left university.
Speculation over an engagement was sparked in February 2006, when it was suggested she would receive her own royal security.Media scrum
In December 2006, Catherine was again in the headlines after she and her mother attended a ceremony at Sandhurst Royal Military Academy, to watch Prince William being commissioned as an army officer.
The occasion was notable as the first time she had been seen at a high-profile public event attended by the Queen and other senior royals.
Rumours of an engagement reached a peak around the time of Catherine's 25th birthday in January 2007, when the media scrum took up residence outside her Chelsea home.
The paparazzi free-for-all drew inevitable comparisons with the prince's late mother, killed in a car crash in Paris while being pursued by photographers.
Prince William and Prince Charles appealed for her to be left alone, and some newspapers agreed to stop using paparazzi shots of her.
In March, Catherine's lawyers made an official complaint to the Press Complaints Commission over a photo published in the Daily Mirror.
It showed her clutching a takeaway coffee cup and car keys as she headed to work. The Mirror issued a public apology and the complaint was withdrawn.
Media pressure appeared to take its toll and was blamed when the couple split in April 2007, although no official statement was issued by either.
Reports of a reconciliation were denied in June 2007, with the couple insisting they were "just good friends" after being spotted together at the Concert for Diana at Wembley.
They were then seen in public on a number of occasions.
Catherine was present when the prince received his RAF wings from his father at RAF Cranwell in April 2008 and in Windsor when he became a Knight of the Garter in June.Royal baby
The couple announced their engagement in November 2010, and at the time Catherine said joining the Royal Family was a "daunting prospect".
"Hopefully I'll take it in my stride," she added.
Since her marriage, the duchess has become the patron of four charities: Action on Addiction, East Anglia's Children's Hospices, the Art Room and the National Portrait Gallery.
She and Prince William have undertaken two official overseas tours - to North America and Canada in 2011, and to South East Asia in 2012 to mark the Queen's Diamond Jubilee.
In September last year, the royals took legal action against a French magazine that published topless pictures of the duchess, taken during a private holiday.
In December, St James's Palace announced that the Duchess of Cambridge was expecting a baby, and that Catherine had been admitted to hospital with acute morning sickness.
She stayed in hospital for several days before being released, but her stay was marred by the suicide of nurse Jacintha Saldanha after two Australian DJs made a hoax call to the hospital.
Carrying out her final royal engagements in June, she then withdrew from the public eye ahead of the birth.
Baby Prince George was delivered on 22 July at 16:24 BST, weighing 8lbs 6oz, in the private Lindo Wing of St Mary's Hospital in Paddington, west London - where Princess Diana gave birth to her sons.
The couple spent the first few years of married life on Anglesey, north Wales, where the Duke of Cambridge worked as a search and rescue pilot with RAF Valley.
But, with the announcement that the duke is leaving the military, the couple are expected to leave the island to set up home in an apartment in Kensington Palace, London.