William, Harry and Pippa at society wedding minus Kate
As the final countdown to the birth of her baby begins, the Duchess did not attend the ceremony.
The Duke of Cambridge and his brother Harry were among the first guests to arrive at the society wedding of one of their best friends.
Under sunny skies, they were in a large male group accompanying groom Thomas van Staubenzee who is marrying the Duke of Northumberland's daughter Lady Melissa Percy.
Well-wishers lined Alnwick's Bailiffgate from the Percy family's 1,000-year-old castle, which has served as Hogwarts in the Harry Potter films, to St Michael's Parish Church.
Harry followed the groom in the group that walked with Mr van Straubenzee, with William just behind.
The crowds cheered as they made their way to church ahead of the 5pm wedding. The Duchess of Cambridge, eight months pregnant, will not be among the 500 guests.
Before the wedding, the Duchess of Northumberland, mother-of-the-bride, told The Journal newspaper: "We are really excited. The weather forecast is not great but Melissa and Thomas do not seem to mind.
"Whatever the weather it is going to be a wonderful day."
Lady Melissa is a 26-year-old tennis coach while the groom is a chartered-surveyor and long-time friend of both William and Harry.
The brothers were at the 30-year-old's London stag do earlier this month. Mr van Straubenzee travelled to New Zealand with William on a gap year and was reportedly on the phone to Harry when he was mugged in London last year. It was said that Harry alerted police and went out to find his friend after the ordeal.
Lady Melissa is the Duke of Northumberland's second daughter. When her sister Lady Katie, a motorbike mechanic, married at St Michael's Church two years ago, Pippa Middleton was a guest. She is friends with Earl George Percy, the Duke's elder son.
Chelsy Davy, Harry's former girlfriend, will also be there to attend to the bride who will leave Alnwick Castle in a restored horse-drawn carriage that is almost 200 years old. She will wear a Bruce Oldfield dress with flowers by local florist Caro Dickinson, who has also decorated the church and castle.
After the service, a reception will be held in the castle's State Rooms, followed by dinner in a marquee. There will be fireworks in the evening which the public can watch from the Pastures below the castle. Soon after the wedding, Lady Melissa's dress will be displayed alongside her sister Katie's wedding dress in The Coach House at Alnwick Castle.
Pippa Middleton was greeted at the church gates by cries from the crowd of "beautiful". She wore a blue and white floral dress with a hat. Tara Palmer-Tompkinson had a little trouble as a gust of wind threatened to blow off her hat. She wore a blue and white striped suit. Some of the male guests wore spats-type shoes for the posh event.
Princesses Beatrice and Eugenie added to the Royal contingent at the wedding. Eugenie, in green, and Beatrice, in blue, were met with calls of "gorgeous" from the crown. They hugged other guests at the gate before walking into the pretty church.