A woman has been arrested on suspicion of attempted burglary at Prince George's school, just a week after he started there.
Police and royal security teams are now urgently reviewing their arrangements at Thomas's Battersea in south London.
A Metropolitan Police spokesman said: "The arrested woman was taken to a south London police station where she remains in custody.
"We are working with the school, which is attended by His Royal Highness Prince George, to review its security arrangements after the incident.
"Police were alerted and officers attended immediately after the issue came to light.
"Police are part of the protective security arrangements for the Prince and we will continue to work closely with the school, which is responsible for building security on its site."
Prince George was understood not to be at the independent school at the time.
Kensington Palace said: "At the time of the arrest, the reception classes had left for the day. He will be attending class tomorrow."
- Prince George, four, only started at the fee-paying independent school last week, on September 7
- He was expected to begin by attending school for half-days, before building up to longer hours
- It educates 560 boys and girls aged from four to 13, with around 20 pupils in each class
- Fees cost £17,604 a year, and increase to £19,884 a year for those in year three and above