Typically, the Queen is the first to know about the baby's birth and an official announcement is placed on an easel outside Buckingham Palace.
A royal baby is also usually christened in a private baptism around three or four months after his or her birth, but this is one tradition Eugenie could decide to break.
WATCH: A timeline of Eugenie and Jack's love story
Princess Eugenie was baptised at St Mary Magdalene Church in Sandringham in December 1990 and she was the first royal baby to have a public christening.
While the media and members of the public have gathered outside churches to see royal christenings in recent years, the ceremony has taken place behind closed doors.
The Cambridges arriving at Princess Charlotte's christening in 2015
Photographers captured the arrival of the Duke and Duchess of Cambridge for their sons Prince George and Prince Louis' christenings at the Chapel Royal in St James's Palace in 2013 and 2018 respectively, while locals gathered to greet the royals at Princess Charlotte's baptism in Sandringham in 2015.
However, the christening service itself was not broadcast to the public.
The royals at Eugenie's christening in 1990
Eugenie and Jack, who celebrated their second wedding anniversary last October, announced their baby news with an adorable Instagram post. It featured photos of the parents-to-be beaming at the camera together and holding a pair of John Lewis bear slippers. The Princess, 30, wrote: "Jack and I are so excited for early 2021..."
The official statement from Buckingham Palace read: "Her Royal Highness Princess Eugenie and Mr Jack Brooksbank are very pleased to announce that they are expecting a baby in early 2021.
"The Duke of York and Sarah, Duchess of York, Mr and Mrs George Brooksbank, The Queen and The Duke of Edinburgh are delighted with the news."
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