According to news.com.au, the Duke and Duchess of Cambridge were gravely "concerned" that Benjamin managed to gain access to not just Prince George, but Princess Charlotte and Prince Louis as well.
Benjamin was involved in a brutal torture plot in 2008, where he poured boiling water down the back of an innocent man.
According to news.com.au, Darren Benjamin was delivering furniture to Kensington Palace on July 14 and was greeted by George, seven, Charlotte, four, and Louis, one, who were in the courtyard with their nanny Maria Teresa Borrallo.
A source told news.com.au: “This is the type of potentially deadly security oversight that simply cannot be allowed to happen.
“Darren is a violent criminal who was jailed for the most brutal type of torture.
“It’s chilling as he has been boasting to friends about just how close he came to our future king and the other Cambridge children.
“His friends were shocked that he was able to get into the Palace and within touching distance of royalty given his past.”
Buckingham Palace has released the following statement: “The Duke [Prince William] has been informed and is obviously taking a close interest into what happened.
“He strongly believes criminals deserve a second chance once they have served their time, but is concerned current security policies might not be strong enough.
“It’s very important we know who is coming into the Palace.”