But fans have a number of questions about the future addition to the Sussex household.
Unlike previous royal babies, who have usually been welcomed into the world at St Mary’s hospital or Portland Hospital in London, the incoming child is likely to be born somewhere in California, where the young family lives.
Given this will be the first American-born British royal baby in history, some are questioning what citizenship baby Sussex 2.0 will have when he or she arrives.
Wherever it’s born, UK and US laws indicate the baby will be eligible to receive dual citizenship either way because its parents are British and American, respectively.
Another area of uncertainty is whether the baby will have a royal title since the Duke and Duchess of Sussex stepped down as senior royals in January 2020.
Considering Archie did not receive a royal title when he was born in May 2019, it is unlikely his younger sibling will.
Traditionally, royal titles are granted on wedding days, as in the cases of Prince Harry’s Duke of Sussex title and Prince William’s Duke of Cambridge title.
Archie also deliberately missed out on a Prince title.
At seventh in line to the throne, his grandmother Queen Elizabeth could have given him a courtesy title of prince, but the Sussexes reportedly turned it down.
This is because Prince Harry and Markle intentd to give their firstborn a normal and fiercely private upbringing.
The second Mountbatten-Windsor bairn will also likely skip the prince or princess title, though like Archie, they could be eligible for one when they turn 18.
Despite their parents officially stepping down as working royals, Archie and his sibling will keep their ranks as seventh and eighth in line to the throne.
The announcement comes a few days after Prince Harry’s cousin Princess Eugenie gave birth to her first son with her husband Jack Brooksbank.
Baby Brooksbank, whose name has yet to be revealed, was 11th in line to the throne for the first few days of his life, before quickly being bumped to 12th following news of Markle’s bun in the oven.
Currently, the Queen’s eldest son Prince Charles, 72, is first in line, followed by his son Prince William.
Prince William’s children, seven-year-old Prince George, five-year-old Princess Charlotte and two-year-old Prince Louis are next in line, followed by Prince Harry who is sixth in line, then Archie and his soon-to-be younger sibling.
The Queen’s disgraced second son, Prince Andrew, is next.
Announced on Valentine’s Day as a nod to Princess Diana who shared her baby news on the same day 37 years ago, the happy news comes just months after Markle revealed she suffered a miscarriage in July.
“Losing a child means carrying an almost unbearable grief, experienced by many but talked about by few,” Markle wrote in an essay for The New York Times in November.