The mother of Charlie Gard, who is fighting for the right to take her dying baby to the US for treatment, has broken down in court.
The High Court judge halted proceedings as Connie Yates sobbed whilst hearing medical evidence about her son's condition.
Earlier Mr Justice Francis said he understood the parents were in "an almost impossible situation".
Charlie's mother, Miss Yates, and his father, Chris Gard, have raised over £1.2m to send him for pioneering treatment in America.
Doctors at Great Ormond Street Hospital, however, say he should be moved from life support treatment to palliative care and allowed to die with dignity.
Giving evidence a doctor, who can't be identified, said Charlie was no longer responsive and it was "really difficult to be certain" if he was in pain or not.
He told the judge the eight-month old's condition had "deteriorated hugely" and he was "completely ventilator-dependent".
The doctor also said the situation "was not a tolerable one to keep a child in".
Mr Gard, who sat in court with a monkey teddy bear in his suit jacket pocket, visibly upset throughout, told the judge:
"My son is the apple of my eye. I would do anything for him and I just want him to be given a chance, he deserves a chance."
He said he and Charlie's mother believed their son "knows who we are" and "can sense who we are".
"We firmly believe that Charlie was sent to us because we were the ones to look after him," he said, "we were the only ones to look after him."
He went on to say: "We are not doing this because we can't bear to lose him...we just want that chance for him to improve and have a better quality of life."
Charlie's mother broke down and apologised before leaving court for 10 minutes after the judge called for a break.
Returning to give evidence, Miss Yates said: "I don't think he is suffering or I wouldn't be here now. If I felt he was suffering there wouldn't have been an application."
She admitted the treatment offered the US was "a treatment and not a cure".
She went on to tell the judge: "I promise you if he doesn't improve we will let him go."
In a hearing on Monday, a US medical expert said there was a "small chance" that treatment could improve brain function.
Charlie suffers from a rare genetic condition called mitochondrial depletion syndrome which causes progressive muscle weakness.
He was born a healthy baby on 4 August 2016 but by eight weeks old he was losing weight and strength.
He was admitted to Great Ormond Street Hospital in October.
His parents say they want to give him a chance by taking him to the US for treatment called nucleoside therapy.
Mr Justice Francis will have to make a decision based on Charlie's best interests.