Pippa Middleton

Pippa Middleton and James Matthews departing after attending a Christmas Day service at St Mark's Church in west London on December 25, 2016.

Pippa Middleton smiles as she travels in a Semi-State Landau in London after the wedding service for Prince William and Kate, April 29, 2011.

Pippa Middleton arrives at the West Door of Westminster Abbey in London for the wedding of Prince William and her sister, Kate Middleton on April 29, 2011.

Pippa Middleton sits in the Royal Box on Centre Court on day four of the 2012 Wimbledon Championships tennis tournament at the All England Tennis Club in Wimbledon, southwest London on June 28, 2012.

From left, Pippa Middleton and Kate Middleton watch Roger Federer of Switzerland face Andy Murray of Britain during the men's final match at the All England Lawn Tennis Championships at Wimbledon, England on Sunday, July 8, 2012.

Pippa Middleton seen at the The Fayre of St James Charity Concert presented by the Quintessentially Foundation at St James's Church in London on Thursday, Nov. 29, 2012.

From left, Carole Middleton and Pippa Middleton watch the tennis match between Britain's Andy Murray and Nicolas Mahut of France, on the center court at Queen's Club grass court championships in London on Thursday, June 13, 2013.

Pippa Middleton arrives at a bookshop to promote her new book "Celebrate: A Year of British Festivities for Families and Friends," in London on Thursday, Oct. 25, 2012.

Pippa Middleton poses for photographers as she attends the UK premiere of the film "Shadow Dancer" at a central London cinema on Monday, Aug. 13, 2012.

Pippa Middleton watches Sweden's Robin Soderling play France's Gilles Simon during their fourth round match of the French Open tennis tournament at the Roland Garros stadium in Paris on Monday, May 30, 2011.

Pippa Middleton arrives at the wedding of the Duke and Duchess of Northumberland's eldest daughter Lady Katie Percy to city financier Patrick Valentine at St Michael's Church in Alnwick, England on Saturday, Feb. 26, 2011.

Pippa Middleton leaves after attending the wedding of the Duke and Duchess of Northumberland's daughter Lady Melissa Percy to chartered surveyor Thomas van Straubenzee at St Michael's Church in Alnwick, England on Saturday, June 22, 2013.

From left, siblings Pippa Middleton and James Middleton await the start of play on Centre Court at the All England Lawn Tennis Championships in Wimbledon, London on Monday, June 24, 2013.

Pippa Middleton arrives at the wedding of James Meade and Lady Laura Marsham at Gayton Church in Gayton, Norfolk on Saturday, Sept 14, 2013.

Pippa Middleton, second left, and broadcaster Ben Fogle, second right, arrive for the Sir David Frost memorial service at Westminster Abbey in London on Thursday, March 13, 2014.

Aberdeen Asset Management congratulates Pippa Middleton and the Michael Matthews Foundation team as they complete the Race Across America (RAAM) early this morning in Annapolis, Maryland on June 21, 2014.

Pippa Middleton arrives at the Church of St. Mary Magdalene on the Sandringham Estate, England for the Christening of Princess Charlotte of Cambridge on Sunday, July 5, 2015.

Pippa Middleton arrives for the GQ Men of the Year Awards 2014 at a central London venue on Tuesday, Sept. 2, 2014.

Pippa Middleton watches the quarterfinal tennis match between Canada's Milos Raonic and France's Gilles Simon on the fifth day of the Queen's Championships in London on Friday, June 19, 2015.

Pippa Middleton takes her seat in the Royal Box on Centre Court, ahead of the women's semifinal matches, at the All England Lawn Tennis Championships in Wimbledon, London on Thursday July 9, 2015.

Pippa Middleton sits in the Royal Box on day eight of the Wimbledon Tennis Championships in London on Monday, July 4, 2016.

Pippa Middleton finishes the London to Brighton Bike Ride for British Heart Foundation in Brighton, England on June 21, 2015.

Pippa Middleton sits in the Royal Box on Centre Court on the first day of the Wimbledon Championships at the All England Lawn Tennis Club, in London on June 27, 2016.

From left, Pippa Middleton, James Middleton, and actress Rebel Wilson sit in the Royal Box before the match between Novak Djokovic of Serbia and Jamie Ward of Britain, during day one of the Wimbledon Tennis Championships in London on Monday, June 27, 2016.

Pippa Middleton, sister of Catherine, Duchess of Cambridge attends the Aegon tennis Championships at the Queen's Club in London, Britain on June 10, 2014.

From left, Pippa Middleton and Spencer Vegosen watch Victoria Azarenka of Belarus (1) against Samantha Stosur of Australia (7) during their 2012 US Open women's singles match at the USTA Billie Jean King National Tennis Center on Sept. 4, 2012.

Pippa Middleton watches a match on day eight of the ATP World Tour Finals tennis tournament in London on Nov. 27, 2011.

Pippa Middleton watches Czech Tomas Berdych play against Switzerland's Roger Federer during the 2012 U.S. Open on Sept. 5, 2012.

Pippa Middleton attends the wedding of Katie Percy in Alnwick, England. on June 13, 2011.

Pippa Middleton moments after crossing the finish line of the 88th Vasaloppet cross country ski marathon in Sweden on March 4, 2012.

Maid of honor Pippa Middleton follows her sister into Westminster Abbey during Catherine's wedding to Prince William last year on April 29, 2011.

Pippa Middleton holds sister Catherine's train during her wedding to Prince William last year on April 29, 2011.

Maid of honor Pippa Middleton arrives with ring bearers during the royal wedding of Prince William and Catherine Middleton last year on April 29, 2011.

Pippa Middleton watches a tennis match at the AEGON Championships in London last year on June 9, 2011.