The parents of Jack Letts' are on trial accused of funding terrorism.
A Muslim convert dubbed Jihadi Jack ranted about decapitating an old school friend after finding out he was in the British Army, a court has heard.
Despite Jack Letts' apparent online outburst about Linus Doubtfire, his supportive parents still tried to help him, the Old Bailey was told.
Organic farmer John Letts, 58, and his wife Sally Lane, 56, are on trial accused of sending or trying to send sums totalling £1,723 to their son even though they had every reason to believe he had joined Islamic State in Syria.
His mother, a former fundraising and marketing officer, had bought him a flight to Jordan, despite a warning that he planned to go and fight in Syria, the court heard.
Jack Letts left his family home in Oxford in 2014 aged 18.
From there, he travelled to Kuwait and then on to Iraq and Syria, the jury was told.
On October 1 2014, Lane told one of her son's friends he was "OK for now" but "in the worst place possible and doesn't want to leave".
The next day, Letts revealed to a friend that he was "over there" in an "Isis area" but not fighting.
He allegedly said: "It sounds like he's having the adventure of a lifetime."
By early 2015, the defendants knew their son had married in Iraq and had no intention of returning to Britain, jurors heard.
John Letts accused his son of lying about his plans to leave and said he was a "pawn... helping to spread hatred, pain, anger, suffering and violence".
In March 2015, police visited the defendants and formally warned them they risked prosecution if they sent their son property or money, jurors were told.
When he found out about the raid, Jack Letts allegedly responded: "Please convey to the British police that I'm not planning on coming back to their broken country.
"Convey to them from me 'Die in your rage soon you'll be the ones being raided!'"
In May, he posted a picture of himself standing on the Taqba Dam in Raqqa, the heartland of IS territory, jurors were told.
In July, Mr Doubtfire posted a picture on Facebook as he completed his Commando Artillery Course in the British Army.
Letts commented: "I would love to perform a martyrdom operation in this scene."
Prosecutor Alison Morgan QC said the defendants appeared shocked by his Facebook post.
Lane allegedly urged him not to be "so stupid", saying: "How did we bring you up to be so easily manipulated?"
He responded: "I admit it was wrong if I seemed like I was joking. I genuinely believe attacking the British Army is a very praiseworthy action when the intention is correct.
"I would happily kill each and every one of Linus Unit personally.
"This message for you, Mum and (younger brother) Tyler, I honestly want to cut Linus head off.
"I hope he finds himself lost in Beji or Fallujah one day and sees me whilst I'm armed and I put six bullets in his head."
His mother replied: "I'm really hoping that your disgusting comments about cutting people's heads off are not coming from you, i.e. someone else is using your account."
Ms Morgan said the significance of the exchange was that the defendants were never sure they were communicating directly with their son, let alone that the transfers they went on to make would go to him or what the money would be used for.
On September 2 2015, Lane allegedly transferred money to an account in Lebanon after her son insisted it had "nothing to do with jihad".
She allegedly told him: "I would go to prison for you if I thought it gave you a better chance of actually reaching your 25th birthday."
In October, she told him: "Clearly I indulged you, I made you think you were the centre of the universe. I regret this bitterly.
"I was a terrible parent that gave you too much power as a child - I should have made you adapt to the world, instead of adapting myself to your world. I have done you no favours by doing this."
She said he showed signs of "mental illness", adding: "I have to bear some responsibility for that as your mother."
In a police interview in November, Lane denied helping terrorists, saying she hoped the money she sent would pay for her son to get glasses.
In December 2015, Jack Letts urged his mother to send him more cash, saying he wanted to leave, the court heard.
John Letts berated his son, saying: "Why should I risk going to jail for helping a 20 year old who is acting like a spoiled child rather than a man."
But on December 27, he contacted a police liaison officer, claiming his son was "desperate to get out" and "in danger" because he had made a break from IS.
He was mistakenly advised by the officer that if there was a genuine belief Jack Letts needed help to leave Syria, he could send funds.
But jurors were told that other officers quickly clarified that the defendants did not have permission.
Despite the risk of arrest, Lane allegedly attempted to send £1,000, saying: "We know you are in danger so we feel we have no choice but to help you and send it. You have to use it to get out as we don't want to support ISIS."
Later, she asked Jack Letts to confirm if he was in danger, to which he replied: "Define danger."
When they discovered the transfer had been blocked, the defendants allegedly tried to make two transfers of £500 using false details, jurors heard.
The money was again blocked and the defendants were subsequently arrested.
John Letts and Lane, of Chilswell Road, Oxford, have denied three charges of funding terrorism.
The trial continues.