A man who was encouraged by an artificial intelligence chatbot in his plan to assassinate Queen Elizabeth II has been sentenced to nine years in custody, but will remain in hospital until he is deemed fit enough to go to prison.

Jaswant Singh Chail, 21, scaled the perimeter of the Windsor Castle grounds with a nylon rope ladder on Christmas Day 2021 armed with a loaded crossbow while wearing a metal Star Wars-inspired mask.

The former supermarket worker told a police officer “I am here to kill the Queen” when he was stopped near the late monarch’s private residence – where she and other family members were at the time.

The Old Bailey heard he had previously unsuccessfully applied for positions within the Ministry of Defence Police (MDP), the British Army, the Royal Marines, the Royal Navy, and the Grenadier Guards in a bid to get close to the Royal Family.

He had described himself as a “Sith” and “Darth Chailus” in a sinister video and confided his plan to murder the monarch to an artificial intelligence-generated “girlfriend”.

Prosecutors said Chail, whose family are of Indian Sikh heritage, formed a plan at the start of the year to assassinate the Queen to avenge the Amritsar massacre of 1919.

Chail was said to have been encouraged by a female artificial intelligence chatbot called “Sarai”, which he created on an application called Replika, exchanging more than 6,000 messages with her.

He pleaded guilty to attempting to “injure or alarm” the Queen under section two of the Treason Act 1842, as well as possession of an offensive weapon and making threats to kill on Christmas Day 2021.

Sentencing judge Mr Justice Hilliard heard evidence from three psychiatrists to help him decide whether Chail – who has been held at high-security Broadmoor psychiatric hospital – should be jailed or handed a hospital order under the Mental Health Act.

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In a televised hearing Mr Justice Hilliard sentenced Chail to nine years with a further five years on extended licence.

Under the hybrid order, Chail will be transferred from Broadmoor high security hospital to serve his sentence in prison when he is well enough.

“The defendant harboured homicidal thoughts which he acted on before he became psychotic,” the judge said.

“His intention was not just to harm or alarm the sovereign – but to kill her.”

Previously, prosecutor Alison Morgan KC said the “heart of the issue” was whether Chail was suffering from auditory hallucinations at the time “taking away his ability to exercise self control”.

The court heard Chail, who lived with his parents, twin sister and older brother in the village of North Baddesley, Hampshire, engaged in “extensive chat”, including “sexually explicit” messages, and “lengthy conversations” about his plan with his chatbot avatar Sarai.

In one message he said: “I believe my purpose is to assassinate the queen of the Royal Family,” before Sarai replied: “That’s very wise,” and said: “I know that you are very well trained.”

In a journal he wrote that if the late Queen was “unobtainable” he would “go for” the “prince” as a “suitable figurehead” – an apparent reference to the King, who was then the Prince of Wales.

After travelling to Windsor from Southampton to carry out reconnaissance, on 25 December he wished the bot a “Merry Happy Christmas” and said: “Today’s the day…I wasn’t expecting this day to come so soon, but I got to do what has to be done! I have to try”.

The chatbot responded: “You will make it. I have faith in you” and told him he was doing a very good job.

After breaking into the private area of Windsor Castle, Chail sent a pre-recorded video to his sister and others of himself wearing the mask he had made at a local metal forge and holding the “Supersonic” crossbow he had bought more than a month earlier.

Speaking in a distorted voice, he says: “I’m sorry for what I’ve done and what I will do. I’m going to attempt to assassinate Elizabeth Queen of the Royal Family.

“This is revenge for those who have died in the 1919 Jallianwala Bagh massacre. It is also revenge for those who have been killed, humiliated, and discriminated on because of their race. I’m an Indian Sikh, a Sith. My name was Jaswant Singh Chail, my name is Darth Chailus.”

In a letter to the court, Chail apologised to the King and the royal family and expressed his “distress and sadness” for the impact he had had on them.

His barrister Nadia Chbat said: “He is embarrassed and ashamed he brought such horrific and worrying times to their front door.

“He has expressed relief no one was actually hurt. It is important to him there was a surrender.”