Pippa Middleton steps up the glamour in a leggy black dress as she parties with brother James's new girlfriend Donna Air

She leaped to worldwide fame due to her derriere at the Royal Wedding two years ago.

However, it looks like Pippa Middleton is showing her bottom isn't her only asset as she flashed her toned and tanned legs in a sexy slit dress on Tuesday night.

As she was pictured with brother James and his new girlfriend Donna Air for the first time, perhaps Pippa wanted to up the glamour so she wasn't outshone by the new addition to their social set.

Working it: Pippa Middleton steps up the glamour in a little black dress as she attends the launch of Mr Fogg's bar with boyfriend Nico Jackson

Getting to know the in-laws: Pippa's brother James attended with his new girlfriend Donna Air

Along with her own boyfriend Nico Jackson, the Middletons and Donna joined Princess Eugenie and her beau Jack Brooksbank at the launch of new Mayfair bar Mr Fogg's.

Waitrose columnist Pippa, 29, certainly went for a sexier look than usual, daring to swap her usual knee-length skirts or dresses for a side split which showed off a lot of thigh.

She teamed her dress with a pair of tan high heels and a simple blowdry.

Showing some leg: Pippa ditched her usual knee-length style to show off some thigh

Part of the royal circle: Princess Eugenie also attended with her boyfriend Jack Brooksbank

She was complemented by her 35-year-old stockbroker boyfriend, who looked just as tanned as the Duchess of Cambridge's younger sister.

Meanwhile, Donna, 33, was yin to Pippa's yang in a white dress as she held hands with her toyboy James, 26, as they left the club.

Eugenie, 23, had also opted for similar shades in a white dress with black lace detail, which she teamed with a pair of wedge heels.

Bronzed and bronzer: The couple seemed to have matching glowing tans

Feeling peckish: After attending the launch, the new couple headed to Hunan Chinese restaurant in Belgravia

Although Pippa is already said to made Donna's acquaintance some time ago, it is the first time they have been photographed in public.

However, Donna and James were already pictured partying with Eugenie and Jack back in March at socialite Heather Kerzner's birthday party.

The Geordie model already seems comfortable with the royal circle after she was out partying with Eugenie's sister Beatrice and her boyfriend Dave Clark at Lou Lou's last Thursday night.

Moving on: Pippa and Nico leave the party at a reasonable hour

Pippa's not the only one who can show some leg! Donna's short dress also showcased her fabulous legs

Still going strong: Pippa and Nico's romance went public this winter

The fact Donna and James have been photographed with his family for the first time suggests their romance is stepping up a gear.

The pair quietly started dating in February after meeting at Robin Birley’s private members’ club, 5 Hertford Street in Mayfair.

They finally went public in late April and have since been spotted on romantic walks in Kensington Gardens.

Burgeoning romance: Donna and James only recently went public as a couple following a secret three month romance

Black and white: The 23-year-old royal wore a black and white dress and wedge heels

Hot new venue: The party was to mark the launch of new Mayfair club Mr Fogg's in Bruton Street

However, neither Nico or Donna were at their respective lovers' sides when the Middletons attended the society wedding of Verity Evetts and Christopher Buchanan in Hampshire on Sunday.

While Nico has rarely been at Pippa's side since their romance first went public this winter, perhaps it's too early for James and Donna to make such a statement as a couple.

Former Byker Grove actress Donna famously had a long-term relationship with millionaire Damian Aspinall, father of her nine-year-old daughter, Freya.

What's so funny? Eugenie and Jack seemed in high spirits as they left the new Mayfair bar

Willing escort: While Nico was happy to party on Tuesday night, he was notably absent as Pippa attended a society wedding on Sunday

Meanwhile, James lives rent-free with Pippa in Chelsea in a flat bought by their parents Carole and Michael.

He works for his parents’ party products website in Berkshire, as well as running his Cake Kit Company, which produces cake-making kits and novelty cakes.

Out of all the couples, Eugenie and Jack are the longest term, having dated since 2010.