Princess Kate's sister, Pippa Middleton Matthews, gives birth to baby boy

PHOTO: Catherine, Duchess of Cambridge attends the wedding of her sister, Pippa Middleton and James Matthews at St Marks Church on May 20, 2017, in Englefield Green, England.PlayPool via Getty Images FILE
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Their aunt, Pippa Middleton Matthews, has given birth to a boy. The newborn is the first child for Middleton Matthews and her husband, James Matthews.

Middleton Matthews, 35, is the younger sister of Princess Kate, 36, the mother of George, 5, Charlotte, 3, and six-month-old Louis.

PHOTO: Catherine, Duchess of Cambridge attends the wedding of her sister, Pippa Middleton and James Matthews at St Marks Church on May 20, 2017, in Englefield Green, England. Pool via Getty Images FILE
Catherine, Duchess of Cambridge attends the wedding of her sister, Pippa Middleton and James Matthews at St Mark's Church on May 20, 2017, in Englefield Green, England.

Middleton Matthews gave birth to her son on Monday at the Lindo Wing of St. Mary's Hospital in London, the same hospital where Kate delivered all three of her children.

She delivered her son, whose name has not been announced, just a few days after she stood out in a dark green dress and heels at Princess Eugenie and Jack Brooksbank's wedding at Windsor Castle.

PHOTO: Philippa Middleton Matthews, center, James Middleton, right, and Pippas husband James Matthews, left, arrive to attend the wedding of Britains Princess Eugenie at St Georges Chapel, Windsor Castle, in Windsor, England, Oct. 12, 2018. Adrian Dennis/Pool via Reuters
Philippa Middleton Matthews, center, James Middleton, right, and Pippa's husband James Matthews, left, arrive to attend the wedding of Britain's Princess Eugenie at St George's Chapel, Windsor Castle, in Windsor, England, Oct. 12, 2018.

She announced the news of her pregnancy in June in the fitness column she writes for Waitrose Weekend, a magazine from the U.K. supermarket chain.

PHOTO: Pippa Middleton attends day eleven of the Wimbledon Tennis Championships, July 13, 2018, in London. Karwai Tang/WireImage/Getty Images
Pippa Middleton attends day eleven of the Wimbledon Tennis Championships, July 13, 2018, in London.

Middleton Matthew's pregnancy news came just a few weeks after Kate gave birth to Prince Louis in April.

She gave birth to her son on the same day Prince Harry and Meghan Markle announced they are expecting their first child.

Middleton Matthews married James Matthews, a hedge fund manager with Eden Rock Capital Management, in May 2017 with her sister and Prince George and Princess Charlotte, who served as page boy and bridesmaid, by her side.

PHOTO: Pippa Middleton arrives with her husband James Matthews for the christening of Britains Prince Louis of Cambridge at the Chapel Royal, St Jamess Palace, London on July 9, 2018. Dominic Lipinski/AFP/Getty Images
Pippa Middleton arrives with her husband James Matthews for the christening of Britain's Prince Louis of Cambridge at the Chapel Royal, St James's Palace, London on July 9, 2018.

The Matthews and their newborn live in London.