Throughout her decades-long service as a monarch, Queen Elizabeth II's safety has been put in jeopardy a few times already. However, the latest holiday break-in is probably one of the scariest encounters as a former bodyguard claims Her Majesty's safety is under threat.

Speaking to The Mirror UK, Princess Diana's former security personnel Ken Wharfe gave the longest-reigning monarch a stern warning about her safety, saying the severity of the recent events should "really cause alarm bells to start ringing."

Despite the 19-year-old man being arrested for his attempt, Wharfe said the security system "could always be beefed up" as it could end in a tragic scenario.

Per Express UK, the royal protection unit's former head Dai Davies applauded the officers who responded to the scene that took place at Windsor Castle, saying the team "did their job and averted a disaster."

However, Davies also noted that security in Her Majesty's Berkshire residence should also have the same strict protocols to prevent future intruders and trespassers.

The Holiday Intruder Arrested

Per the outlet, authorities arrested and detained the 19-year-old man under the Mental Health Act under the suspicion of "breach of trespass of a protected site and possession of an offensive weapon."

Thames Valley Police Superintendent Rebecca Mears released a statement, saying the man remains in custody at the time and other members of the firm have been informed about the shocking news. (via CNN)

The man reportedly brought a crossbow at the time of the incident. Despite his weapon being a lethal object, no laws prohibit the public from using it as it does not require a license.

READ NOW: Chris Noth Spent Holidays Alone After Latest, Explicit Sexual Assault Allegations?

Why is the Queen Staying in Windsor Castle?

Queen Elizabeth II was at Windsor Castle to celebrate the holidays after canceling her plans to celebrate at Sandringham, Norfolk, due to the restrictions of the COVID-19 pandemic.

Other royal family members, Prince Charles and Duchess Camilla were also in the area at the time of the incident.

During the Queen's stay, she delivered her highly-anticipated annual Christmas message. She dedicated her speech to her late husband, Prince Philip, who passed away at the age of 99 earlier this year.

Other Royal Intruders

Even though intrusion into the royal family's properties is not common, the most famous trespasser was Michael Fagan, who illegally entered Buckingham Palace by climbing up the walls.

At the time, 31-year-old Fagan was able to reach the Queen's bedroom. Her Majesty, who was sleeping, was unharmed.

 READ ALSO: Gigi Hadid, Zayn Malik Reconcile Despite Allegedly Assaulting Mom Yolanda Hadid?