• Prince Harry and Meghan Markle greeted Kate Middleton on her birthday privately
  • The Duke and Duchess of Sussex are unlikely to post anything as they did in 2019
  • Middleton had a small birthday celebration with her family in Anmer Hall

Prince Harry and Meghan Markle made sure that Kate Middleton would know that they remembered her birthday.

The Duchess of Cambridge turned 40 years old Sunday. There were rumors that the Cambridges and Sussexes were feuding, especially after the latter's tell-all interview with Oprah Winfrey last year. However, according to royal biographer Christopher Andersen, author of "Brothers and Wives: Inside the Private Lives of William, Kate, Harry, and Meghan," the royal couple based in Los Angeles reached out to Middleton on her special day.

"They did a video call," Andersen told Us Weekly. "They wished her a happy birthday. [It was] very private."

He added, "Harry and Meghan were not about to post anything the way they did two years ago. This time everything was kept private."

In 2020, Kensington Palace released a photo of a smiling Duchess of Cambridge to commemorate her 38th birthday. The Duke and Duchess of Sussex, who were still active on Instagram at the time, commented, "wishing a very happy birthday to The Duchess of Cambridge today!" Today reported.

According to Andersen, 72, Middleton spent her birthday in a "small family affair" with her husband and their three children, Prince George, 8, Princess Charlotte, 6, and Prince Louis, 3, at their Anmer Hall home.

"Kate only has a very small circle of friends," he added.

As for how the duchess might have celebrated the day, he said she has an "interesting" tradition of baking her cake. It's reportedly a "holdover" from her mom, Carole Middleton, who founded their family business Party Pieces that supplies decors and supplies for various occasions.

He noted that it was a "very low-key" party because the royal family has a lot of "big bashes" coming up this year, including Queen Elizabeth II's Platinum Jubilee and her husband, Prince William, hitting his birthday milestone in June.

"The queen has a big thing planned for [William] and he is going to throw something as well," he added. "So, there will be big parties again, if COVID allows anything like that to happen."

British journalist Jonathan Sacerdoti mentioned earlier that Middleton would have a "lower key" celebration. Given the surge in COVID-19 cases in the U.K., Middleton only wanted to set an example for the public.

The Duchess of Cambridge marked her birthday by releasing three portraits captured by Italian fashion photographer Paolo Roversi. Prince William and their three children helped pick one of the birthday photos that the palace released for the occasion.

Prince Harry Meghan Markle and Kate Middleton
Prince Harry, Meghan Markle and Kate Middleton attend the first annual Royal Foundation Forum held at Aviva on Feb. 28, 2018 in London. Getty Images/Chris Jackson