There was no indication from police that Prince George or anyone else at the school was threatened at any point.
London police arrested the woman, who was not identified per department policy, at 2:15 p.m. local time on Wednesday one day after "an individual gained access to its premises," according to the press release on the Metropolitan Police's website.
The woman was arrested "in the vicinity of the school" and was taken to a south London police station where she remains in custody.
"We are working with the school to review its security arrangements after the incident," the police statement said. "Police were alerted and officers attended immediately after the issue came to light."
Prince George, third in line to the throne and son of Prince William and Duchess Kate of Cambridge, started school last Thursday at Thomas's Battersea, a few miles across the Thames River from his family's home at Kensington Palace.Read more at USA Today