Pippa Middleton kisses her new husband James Matthews, following their wedding ceremony at St Mark's Church as the bridesmaids and pageboys walk ahead on May 20, 2017 in Englefield Green, England.
The friend continued, "Pippa and James have always known they wanted children".
However, while they are now both expecting, Kate is due to deliver her baby soon while Pippa's child is arriving in October.
A friend of Pippa declared that the Duchess of Cambridge "could not have been more delighted" after being told that her younger sister was pregnant.
"When Pippa found out she was pregnant, she was obviously thrilled and utterly overjoyed", they said.
Kate, who is days away from giving birth to her third child, was said to be "delighted" by the news her sister was expecting.
Aside from Kate, their parents, Carole and Michael, are also ecstatic about the news and have been looking forward to the newest additions to their growing family.
"It's been a tough few weeks for the two families, so this has provided some much-needed happiness and light relief".
Kate was the second person to find out about her sister's pregnancy.
Pippa and the Duchess of Cambridge at her wedding past year.
The 74-year-old David Matthews was accused of two incidents in 1998 and 1999, according to the Daily Mail. Sources close to the couple noted that during the first few months of marriage, they felt the time was right to expand their family.
"David Matthews categorically denies the allegation and unequivocally contests the untrue and scandalous accusation", a family statement said.