However, Armstrong said that due to delay the "window of opportunity" to treat the child had been lost.
At an emotional hearing, in which lawyers as well as relatives were in tears, Charlie's mother was invited to give a statement before the court.
Legal proceedings will resume Monday.
Health Secretary Jeremy Hunt said although Charlie's case was "sad and complex", this behaviour was "totally unacceptable".
Charlie Gard's parents have made a decision to end their legal fight over the treatment of the terminally-ill child.
The hospital also paid tribute to the family, saying the "agony desolation and bravery of their decision" commands Great Ormond's respect and humbled "all who work there".
The parents of Charlie Gard, Chris Gard and Connie Yates, have withdrawn their legal challenge before the High Court in London, England.
"To let our attractive little Charlie go" is "the hardest thing we'll ever have to do", his mother said.
British doctors believe Gard's brain damage is "severe and irreversible" and have said the baby "may be suffering".
Armstrong said Charlie's parents hoped to set up a foundation and they wanted lessons to be learned from the case.
Charlie and his family had gained support from all over the world as Charlie's "army" fought for him to stay alive.
Charlie's parents, based upon the assessment of the doctors, have opted not to pursue nucleoside therapy, an oral medicine that aims to improve the function of his mitochondrial DNA.
The parents of Charlie Gard, the 11-month-old terminally ill baby at the centre of a legal row over whether his life support should be switched off, have ended their long campaign take him to the United States for experimental treatment. "A whole lot of wasted time", his father Chris Gard said outside the court, where supporters chanted "Justice for Charlie" and waved blue balloons.
Britain's High Court is considering new evidence in the case of Charlie Gard.
Gard and Yates wanted to take Charlie-who has a severe condition called infantile onset encephalomyopathy mitochondrial DNA depletion syndrome-to the US because an anonymous physician there had agreed to provide an experimental treatment known as nucleoside therapy.
Doctors say that the treatment won't help and could cause the child pain.
Dr Michio Hirano, an American neurology expert from Columbia Medical Center in NY who came to London to examine Charlie, was one of those who concluded it was too late for the 11-month old to undergo the experimental NBT therapy.
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