Her bio has since been changed to include both of her children.
"The Duchess of Sussex, born Rachel Meghan Markle, married Prince Harry at St George's Chapel, Windsor in May 2018," it now reads. "The Duke and Duchess have two children, Archie Mountbattern-Windsor and Lilibet Mountbatten-Windsor."
Some think the delay was an intentional snub, as after Lilibet's birth, it took seven weeks until she was added to the official line of succession, where she sits in the eighth position, right behind her big brother.
In comparison, when Archie was born, it took a mere two weeks for the website to be updated, and at the time, Harry and Meghan were still active members of the royal family.
When Kate Middleton and Prince William welcomed their third child, 3-year-old Prince Louis in 2018, it took just 12 days for the succession line to be updated.
"The succession to the throne is regulated not only through descent, but also by Parliamentary statute," the royal website states. "The order of succession is the sequence of members of the Royal Family in the order in which they stand in line to the throne."
According to The Mirror, a Buckingham Palace spokesperson has stated that the website is "updated periodically."
"You have got to ask what has taken them so long. All they have got to do is hit the paragraph button and put in a different number," ITV’s Chris Ship noted of baby Lilibet's delay to the succession line.
"They must have done it before. They did it for Archie," he continued. "Clearly they did it for Louis when he was born. And they have done it for some of the other children like [Princess Eugenie's son] August that have been born as well."