Pippa Middleton & James Matthews Wed — What a Gown!

Kate Middleton's sister Pippa exchanged vows with financier James Matthews in a private ceremony at St. Mark's Church in Englefield Saturday — and her gown is threatening to break the stiff upper lip of the Internet!

The princess-worthy, lacy custom gown was the creation of Giles Deacon, boasting a cap sleeve and high neckline. Its corseted bodice gave way to a "heart" detail in the back, completing the gasp-inducing effect.

People magazine reports Pippa's gorgeous veil was designed by Stephen Jones, who used fine tulle and embroidered it with pearls. Underneath the veil sat a dainty Madenhair Fern tiara.

The gown looked as seamless as the wedding, which featured Prince William and Kate's children, Princess Charlotte and Prince George, in the party.

Pippa looked stunning, and gave onlookers a huge smile before heading into the church. Kate could be seen helping her sister with the flowing gown as she passed.

Pippa, who had been the center of much attention at her sister's wedding in an instantly iconic Alexander McQueen gown, definitely continued to make fashion waves with the choices she made on her own wedding day!