An armed man was arrested after attempting to break into Windsor Castle where the Queen was celebrating Christmas with her family.
Police said the intruder was carrying an offensive weapon but did not break into any buildings on Christmas Day morning.
The suspect was being held in custody and the royals had been informed, Thames Valley police said.
A 19-year-old man from Southampton was arrested on suspicion of breach or trespass of a protected site and possession of an offensive weapon, they added.
Officers from Thames Valley and the Metropolitan police responded to a security breach at around 8.30am within the grounds of the castle in Berkshire.
The Sunday Mirror said the arrest came after security controllers monitoring CCTV spotted a man carrying what appeared to be a crossbow.
The Mail on Sunday said sources suggested the man was armed with a crossbow and used a rope ladder to scale a metal fence.
Police did not confirm what the weapon was and it is not known where exactly the man was on the grounds and how close he got to the castle itself.
Supt Rebecca Mears said: “An investigation is ongoing following this incident and we are working with colleagues from the Metropolitan police.
“The man has been arrested on suspicion of breach or trespass of a protected site and possession of an offensive weapon. He remains in custody at this time.
“We can confirm security processes were triggered within moments of the man entering the grounds and he did not enter any buildings.
“Members of the royal family have been informed about the incident. We do not believe there is a wider danger to the public.”
The Queen was celebrating Christmas at Windsor with Prince Charles and his wife, Camilla, in the first year since the death of her husband, the Duke of Edinburgh.
Charles, Camilla, Edward and Sophie, along with their children Louise and James, attended a church service in St George’s Chapel, in the castle grounds, at 10.45am on Christmas Day.
