The parents of terminally ill Charlie Gard have lost their final legal appeal.

The parents of terminally ill child Charlie Gard have lost a last-ditch bid to fly the 10-month-old boy to the US for experimental treatment.

After unsuccessful legal battles in the UK, British couple Chris Gard and Connie Yates took their fight to the European Court of Human Rights, which on Tuesday declared their application “inadmissible”.

Charlie Gard is thought to be one of just 16 children in the world with mitochondrial depletion syndrome, a fatal, inherited condition that causes progressive weakening of the muscles. He can’t breathe on his own, and he can’t move his arms or legs. His heart, liver and kidneys are affected. He is deaf, and suffers severe epilepsy. He has experienced significant, irreversible brain damage.

Faced with their son’s inevitable decline, Gard and Yates this year raised more than $2million via an GoFundMe campaign in the hope of taking him to the US for experimental trial therapy.

READ: Three judges explain their decision to allow 10-month-old Charlie to die.

But in April, a British High Court judge ruled in favour of specialists at Great Ormond Street Hospital, where Charlie is being treated; the judge concluded it was in the child’s “best interest” that the trip not proceed and that he be taken off life support and allowed to “slip away peacefully”.

That ruling was upheld by the Court of Appeal in May, and now the European Court has declined to intervene.

In a statement, the ECHR said it agreed with British domestic courts that "it was most likely Charlie was being exposed to continued pain, suffering and distress and that undergoing experimental treatment with no prospects of success would offer no benefit, and continue to cause him significant harm."

It also declared it was "appropriate to lift the interim measure" which had required doctors to continue providing life support treatment to the boy until the judges' decision was reached.

Its decision, the court said, was "final".

What do you say to someone who has lost a baby? Post continues below.

According to the BBC, a spokesperson from Great Ormond Street Hospital, where Charlie is being cared for, said the decision marked "the end of what has been a very difficult process" and its priority was to "provide every possible support to Charlie's parents as we prepare for the next steps".

"There will be no rush to change Charlie's care and any future treatment plans will involve careful planning and discussion," the spokesperson said.

Chris Gard and Connie Yates have previously said that if the US trip did not proceed the funds raised on Charlie's behalf would go toward a charity that benefits children with mitochondrial depletion syndromes.