Axel's mother, Linda Peanberg King, told St Pancras Coroner's Court that she and her husband Alistair made contact with the Harmoni centre in the Whittington Hospital in Archway, after their son fell ill on the night of October 30 last year.
Five days later - after consulting at least three doctors - he died from bronchopneumonia.
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The row over parking allegedly started after the local council re-paved a road in Harrow.
The officer, known only as NC32, ducked for cover behind a car as eight rounds were fired directly at him.
The abuse began as the train approached Northwood. The woman carried harassing her victim until the next station.