The high level of vitriol and abuse on the royal family's platforms has meant staff have to spend several hours a week moderating and deleting posts, which include racist and sexist abuse as well as threatening remarks.
While the majority of the material is simply crude or offensive - one narrative favoured by the trolls is that Meghan Markle's pregnancy is "not real" - there have been a handful of direct threats. "They can block certain words, but some of it is quite serious", the source said. Over the course of past year, with hundreds of thousands of comments, there were two or three that were violent threats. "And it's not acceptable to attack other users just because they disagree with you".
Kensington Palace's social media accounts are a vital source of information for fans of the royals and its Instagram page has over seven million followers, while its Twitter account has almost 1.6 million.
"She said that the Palace security had told her that they didn't want people to be able to track Meghan through her friends' phones, but her friends said no, and she got really mad at them".
Reports of a rumoured "feud" between Kate and Meghan has only fuelled the online abuse.
Catherine, Duchess of Cambridge and Meghan, Duchess of Sussex applaud ahead of the Ladies' Singles final match between Serena Williams of The United States and Angelique Kerber of Germany. Some thought it was because she was all for female empowerment, others because she wanted to come across as "one of us".
Sifting thousands of posts about Kate and Meghan each day from some of the palace's 7.1 million Instagram and 1.68 million Twitter followers is proving painful for staff.
Australian Open: Serena Williams is injured at the match ball
Williams chasing a record-equaling 24th Grand Slam title, that will tie her with Margaret Court, said she was looking at winning. The star did not protest and went on to lose the match. "Williams was robbed!" one fan wrote after the game alongside a video .
"Arguments about who looks more appropriate, for example, that turn into personal attacks on other users", they say, citing an example where one user told another to "drink bleach" during an argument.
The source continued: "It's creating a supercharged atmosphere, and everyone can join in, but that are the consequences of this?"
INSIDER found dozens of vitriolic comments in response to Kensington Palace's Twitter and Instagram feeds.
Britain's press has urged social media users to stop the inappropriate criticism of the Duchesses of Cambridge and Sussex.
Meghan Markle is shaking up palace tradition, but not everybody's happy about it, a new report suggests.
HELLO! is today urging our readers to spread the #hellotokindness message across social media and take a stand against online abuse.