The American doctor who hopes to treat Charlie Gard has attended a meeting at Great Ormond Street Hospital (GOSH).
Michio Hirano, a professor of neurology at the Columbia University Medical Centre in New York, will help decide if the 11-month-old goes to the US for treatment.
The 55-year-old specialist flew to the UK as part of the court battle over Charlie's future and was met by the GOSH medical director when he arrived at the hospital.
Dr Hirano has been given an honorary contract from GOSH, which gives him the same status as its own physicians.
This means he can examine Charlie and has full access to his medical records and the hospital's facilities.
A judge ruled that Charlie's mother, Connie Yates, could be present for Monday's discussions about Charlie's treatment with Dr Hirano and other medical experts.
Meetings are scheduled to take place on Monday and Tuesday to talk about Charlie's condition, before litigation resumes.
Charlie's parents hope their son will be allowed to go to the US for a therapy trial for his rare genetic condition, overseen by Dr Hirano.
GOSH specialists say the treatment will not work, and the little boy's life support should be turned off.
His parents, from Bedfont, west London, have already lost battles in the High Court, Court of Appeal and Supreme Court.
They also failed to persuade European Court of Human Rights judges to intervene.
Mr Justice Francis has considered the couple's latest claims at preliminary hearings in the Family Division of the High Court in London over the last few days.
He is due to stage further hearings later this month following this week's specialist gathering.