It's no secret by now that Kate Middleton and Meghan Markle are not the best of friends (opens in new tab), but according to one royal biographer, Middleton had good reason not to be around Markle before her wedding to Prince Harry (opens in new tab): She was worried about Prince Louis' (opens in new tab) pregnancy.

Andrew Morton, author of Meghan: A Hollywood Princess (opens in new tab), explains why the two duchesses (opens in new tab) were not really set up to be close: "Kate and Meghan are not sisters or were not friends before joining the royal family, unlike Fergie and Diana," he wrote (via The Sun (opens in new tab)).

"Moreover, during the period of preparation for Meghan's wedding, Kate experienced her third difficult pregnancy and was focused on her own welfare," Morton added. She did not have much energy to bond with her new neighbors."

We don't know how friendly the few interactions they had were, but it makes sense that Middleton would pay close attention to her own health during that period. In all three of her pregnancies, she suffered from hyperemesis gravidarum (opens in new tab) - defined as a pregnancy complication (opens in new tab) that "affects various areas of a woman's health, including homeostasis, electrolytes, and kidney function, and can adversely affect the fetus." Louis was born a few weeks before the Sussex couple's May 2018 wedding (opens in new tab).

"The two women were just getting to know each other when they sat together in the Royal Box to watch the Wimbledon ladies singles final in July 2018," Morton said.

And here's another pretty ironclad reason why the now sisters-in-law never really got together during that period. 'It was more of a practical matter than anything else,' the author continues. Kate spent her weekends and vacations at the Cambridges' country house, Anmer Hall, in Norfolk, while Megan and Harry lived in a large, secluded rental property on the Great Tew Estate in Oxfordshire, about a three-hour drive away."

Morton previously sympathized with Markle (opens in new tab) and said she must be feeling "frustrated" by royal life. He also claimed (opens in new tab) that Prince William's "bullying allegations" drove Markle and her husband to leave the UK.

This article has been updated.