Pippa looked breezy in a lilac wrap dress while out in London.
Pippa attended a book launch in a pretty black dress with lce sleeves.
Pippa attended Sotheby's Summer Party in a bright summery dress.
Pippa wore this black and white belted dress to a book launch party.
Middleton looked beautiful in a beaded gown at a charity gala in London.
Pippa wore an Issa dress to the label's show at London Fashion Week.
The socialite attended the Day-Glo Midnight Roller Disco alongside her sister, Kate, wearing a sequined mini.
Pippa attended the End of Summer Ball in a flowing v-neck gown.
Pippa chose this bright blue frock for the 10th Anniversary celebration of Claridge's Bar.
Pippa wore this stunning white wrap dress to a polo match with white wedges.
Kate's younger sister wore a tiered yellow dress to
Tatler's 300th Anniversary Party.
Pippa added a pop of red to her simple black dress with a bold belt.
Pippa attended a fundraiser in a metallic-embellished dress.
Pippa wore a black tiered jacket and bright pink fascinator to a friend's wedding.
The day before Kate's wedding, the family arrived together. Kate wore a patterned Issa dress while her sister was pretty in pink.
Pippa was dressed in an Alexander McQueen gown for her sister Kate Middleton's wedding to Prince William.
The morning after the Royal Wedding, the Middleton clan left their hotel. Pippa was spotted in bright white pants and a blue Zara blazer.
Pippa accessorized her all-denim look with a neutral bag.
The Duchess' younger sister stepped out carrying her favorite Modalu bag, wearing jeans and a bright pink top.
Pippa chose a blush colored Maje top and carried her Modalu bag while out in London.
Pippa wore a crocheted white dress and a jean jacket to the AEGON Championships.
Out for a shopping trip, Pippa chose a pretty blue and white wrap dress.
Middleton attended a Wimbledon match in a navy version of her crocheted sweater dress.
Pippa met up with friends wearing this casual denim dress by Whistles.
Pippa wore this pretty two-tone Zara dress while out in London.
Pippa dressed up a plaid Maje top with red flats and a Prada messenger bag.
Middleton wore Temperley London's classic fan dress during London Fashion Week.
Pippa stunned in London wearing a tiered silk dress by French Connection with a tan Whistles jacket.
Pippa got coffee with friends in a white Issa dress, adding a pop of color with her Prada bag and matching red flats.
Pippa glowed at the Boodles Boxing Ball in a red gown by Temperley.
The Duchess' younger sister looked pretty in plaid by Zara and black skinny jeans.
Pippa looked chic in a longsleeved LBD, an Alice by Temperley animal-print scarf and a Prada bag.
Pippa attended a charity event in a stunning floral gown by Project D.
Pippa wore a cobalt blue turtleneck dress with a chic black blazer and lace-up booties.
The socialite bundled up in a funnel-neck grey Fay coat and black boots.
We're slightly obsessed with Pippa's blue Sara Berman coat with suede trim which she wore with a black dress and booties.
While out in London, Pippa wore a chic army green Fay coat with black skinny pants and a bag by Loewe.
The royal-in-law wore a snowy white coat with black boots and gloves.
Pippa went for a stroll in bright pink jeans by SuperDry, a plaid Maje top and Zara blazer.
Pippa wore a navy Orla Kiely jacket as she and brother James Middleton smile for the camera.
Pippa attended a Wimbledon match in a navy dress and macramé jacket by Orla Kiely.
Pippa wore this and white Alice Temperley dress to the premiere of
Shadow Dancer, completing the look with strappy heels.
Pippa wore a bright colorblocked Paper London dress to the U.S. Open.
Our favorite royal-in-law went out shopping in NYC carrying a Kate Spade bag, and wearing a casual but bright outfit.
Pippa attended the U.S. Open in a bright yellow Phase Eight frock.
Pippa wore Stella McCartney to promote her book
Celebrate: A Year of Festivities for Families and Friends.
Pippa hosted a Halloween Party for children in London while promoting her book, wearing a brocade Markus Lupfer dress.
She attended a party for W&W Jewellery, a British jewelry company in a metallic skirt and neutral top.
Pippa traveled in style weraing a pretty eggplant coat.
Pippa promoted her book
Celebrate in Amsterdam wearing a bright purple peplum dress by Beulah London.
Pippa looked cozy at the Cheltenham Festival in a Katherine Hooker mustard yellow coat and the same Aquatalia boots her sister Kate loves.
As the new ambassador for the Mary Hare School for the Deaf, Pippa opened the "Murray House" in head-to-toe Tory Burch.
Kate's sister stepped out in London wearing a top and skirt by Sandro, jacket by Alice by Temperley, Alice + Olivia heels, and the Catherine Street Pippa bag by Kate Spade New York.
Pippa attended a party in a pink floral dress by Tabitha Webb.
The middle-Middleton was out and about in silk ikat pants by Alice by Temperley.
Pippa out and about with boyfriend Nico in London, wearing a chic black dress.
Pippa wore a pretty green sweater dress and matching cardigan at the AEGON Championships with her mother Carole.
Attending a friend's wedding, Pippa looked lovely in a black and white peplum Tabitha Webb dress and Olivia Roat Millinery fascinator.
Pippa looked chic in a powder blue blazer over a matching dress at Wimbledon.
Spectator Magazine's summer party in a pretty white lace dress.
Pippa went to another game at Wimbledon with boyfriend Nico, wearing a striped coral dress by Temperley London.
Leaving Andy Murray's match, Pippa looked vibrant in the coral dress.
Pippa attended the Queen's Coronation ceremony in a floral Tabitha Webb dress with a lace overlay, and carried a clutch by Lamb 1887.
Pippa attends the wedding of James Meade and Lady Laura Marsham.
Pippa and Nico Jackson pose at the Boodles Boxing Ball 2013 on September 21, 2013 at the Grosvenor House in London,England.
Pippa attends a donors dinner hosted by Michael Bloomberg & Graydon Carter to celebrate the launch of the new Serpentine Sackler Gallery.
Pippa and James Middleton arrive at Chapel Royal in St James's Palace in central London to attend the christening of Prince George of Cambridge.
Pippa and boyfriend Nico Jackson attend the Sugarplum Ball.
Pippa attends a memorial service for Sir David Frost at Westminster Abbey.
Pippa attends day two of the Aegon Championships at Queens Club.
Pippa Middleton seen arriving at Wimbledon.
Pippa attends the GQ Men of the Year awards.
Duchess of Cambridge
turns 31 today, September 6th.
The London-based writer was launched into the spotlight when she joined her sister's wedding party for the
Royal Wedding in 2011
. When she stepped out in a slinky white Sarah Burton for Alexander McQueen bridesmaid dress she became known around the world as "Her Royal Hotness." Since then, we've become enthralled with Pippa's effortless style.
Pippa also made headlines with
rumors circulating that she was secretly engaged
to her boyfriend Nico Jackson, an announcement that the duo was hoping to keep quiet until this week (so as to avoid overshadowing her sister's news). We were hoping it was true, but turns out the couple are
Click through the gallery to see Pippa's style transformation, and wish her a happy 31st!
Kate Middleton's Style Transformation: All of her Best Royal Looks