A British man who broke into Windsor Castle Christmas Day 2021 and threatened Queen Elizabeth with a crossbow has pleaded guilty to treason charges Friday in a London court.

Appearing before London's Old Bailey Court via video link, 21-year-old Jaswant Singh Chail of South Hampton pleaded guilty to an offense under the British Treason Act of 1842, and to threatening to kill the queen. Charges under the act are rare, the last person to plead guilty under the act was in 1981.

Prosecutors say Chail was arrested shortly after 8 a.m. Christmas Day 2021 by a royal protection officer on the private grounds of Windsor Castle. Queen Elizabeth, who died in September 2022 at age 96, then-Prince Charles and other family members were staying at the castle during the holidays. Chail was never near the royal family.

At the time of his arrest Chail was dressed in black clothing and wearing a hood, a metal mask, gloves and carrying a powerful crossbow. He reportedly told the protection officer, "I am here to kill the queen."

Prosecutors said Chail had recorded a video and posted it to the social media platform Snapchat before he entered the grounds of the castle. In it, he said he was sorry for what he was about to do. He said it was revenge "for those who died in the 1919 massacre."

He was apparently referring to an incident when British colonial troops opened fire on unarmed civilians protesting a colonial law in their holy city of Amritsar in northwestern India. Nearly 400 Sikh Indians were killed in what has become known as the 1919 Jallianwala Bagh massacre. India has long demanded an apology for the incident.

In court Friday, Judge Jeremy Baker scheduled sentencing for Chail on March 31, and the court ordered medical reports regarding Chail's mental state to be provided.

Some information for this report was provided by Reuters.