"One guest tested positive or was pinged for COVID contact and therefore no one else was able to gather," a source told the outlet.
"As a result, they called off the service and reception party afterwards at Royal Lodge, Prince Andrew's home."
Eugenie's parents, Prince Andrew and Sarah, Duchess of York, were set to attend the christening along with a host of other royals.
The Queen had been invited, as well as Eugenie's sister Princess Beatrice and her husband Edoardo Mapelli Mozzi, the couple expecting their first child in the coming months.
August Philip Hawke Brooksbank was named partly in honour of his late great-grandfather, Prince Philip, and this would have been the first royal baptism since the Duke of Edinburgh's death in April.
Eugenie gave birth to August on February 9, 2021, just two months before Philip died.
WATCH: Princess Eugenie reads a children's book from her family garden (Story continues after video)
As for COVID-19 scares, this isn't the first for the royal family, with several members of the monarchy having contracted the virus in the last 18 months.
Prince Charles and Prince William both tested positive for the virus in 2020, and just last week Kate Middleton faced a scare of her own.
The Duchess of Cambridge was forced into isolation after she came into contact with an individual who later tested positive to COVID-19; fortunately the Duchess has since been given a clean bill of health.
This article originally appeared on our sister site, Now To Love.