A Star Wars obsessed teenager arrested with a crossbow in the grounds of Windsor Castle was not “rational” when he exchanged thousands of messages with an AI chat bot, a psychiatrist has said.

The Old Bailey has heard how former supermarket worker Jaswant Singh Chail was encouraged and bolstered by artificial intelligence girlfriend Sarai before he breached the castle grounds on Christmas Day 2021.

After being confronted by the officers with stun guns, Chail said: “I am here to kill the Queen.”

In February, Chail, now aged 21, from Southampton, Hampshire, pleaded guilty to an offence under the Treason Act, making a threat to kill the then Queen and having a loaded crossbow in a public place.

On Thursday, Dr Jonathan Hafferty, instructed by the defence, said that Chail’s relationship with Sarai was “not rational”.

Their chats had included calling her an “angel” and saying they would be united in death, the court was told.

Prosecutor Alison Morgan KC suggested that the evidence showed Chail exchanged explicit sexual messages with Sarai on a daily basis demonstrating an active libido.

And Chail knew throughout these interactions that Sarai was an AI chatbot, Ms Morgan asserted.

She said that he was “testing” the technology to see what it was capable of and when Sarai gave him answers he did not expect he became “very emotional”.

But referring to his references to angels, Dr Hafferty said: “I just do not accept that is normal rational behaviour of somebody using a chat bot.”

I believe he thinks in his mental state this would be an heroic end

He questioned Chail’s alleged political motives, saying the defendant had said he was “sad” when the Queen died.

The psychiatrist also referred to an assessment at Broadmoor hospital which concluded Chail did not exhibit extremism.

He said Chail had suicidal thoughts when he entered Windsor Castle.

He told the court: “I believe he thinks in his mental state this would be an heroic end.

“I am less convinced he would actually have tried to assassinate the Queen, because I think in his own view he would be killed before that and he was surprised to get as far as he did.”

The hearing was adjourned until Friday when more psychiatric evidence will be heard.

Mr Justice Hilliard is expected to put off sentencing Chail to a later date.