Kate Middleton
Britain's Catherine Duchess of Cambridge and Prince William (R) in the royal box on Centre Court at the Wimbledon Tennis Championships in London, July 8, 2015. Reuters/Suzanne Plunkett

Kate Middleton, the Duchess of Cambridge, reportedly opted to celebrate her 36th birthday with husband Prince William, their two kids 4-year-old Prince George and 2-year-old Princess Charlotte, and some friends. It was said to be a “low key party” at Kensington Palace.

Although she is part of the British royal family, the pregnant duchess did not throw a big party and preferred a more intimate setting. A source told E! News that Middleton was celebrating privately with her spouse and their kids. “It's just a quiet celebration at home.”

Meanwhile, a source told Daily Star Online that Middleton had a low-key birthday party with only eight invited guests. Middleton was careful with her food and was not drinking alcohol, it has been said.

According to Daily Star Online, married friends Guy Pelly and Elizabeth Wilson were among those who got a birthday invite. Sophie Carter, one of Princess Charlotte’s godmothers and Middleton’s close friend, was expected to be in attendance. It is unclear if Middleton's brother-in-law Prince Harry and his bride-to-be Meghan Markle were at the celebration.

It is not the first time Middleton celebrated her birthday with a private and simple party. Last year, she marked her special day at Anmer Hall in Norfolk with her family and Carter. On her 31st birthday, she went with her siblings and some of her friends to the Royal Albert Hall to watch Cirque du Soleil.

There seemed to be no grand celebration for the Duchess this year, but there are a number of happenings to celebrate. Charlotte just started nursery school on Monday, with Middleton herself taking a photo of her. Two photos of the princess were shared on social media.

In addition. Harry and Markle made their first public appearance in 2018 together. The pair was welcomed by hundreds of fans on Tuesday at a radio station in south London, where they met staff from Reprezent FM, a community radio station that provides training to young people in media skills.

Middleton’s 36th year is expected to be busy as she is due to give birth to her third child in April. Harry and Markle’s wedding will take place in May, and she is expected to be there.