King Charles smiled and waved to passers-by on Tuesday as he was seen in public for the first time since it was revealed he was suffering from a form of cancer and as his estranged younger son Prince Harry flew to Britain to see him.Buckingham Palace announced on Monday that Charles, 75, on the throne for less than 18 months since the death of his mother Queen Elizabeth, had been diagnosed with the disease and would postpone his public engagements to undergo treatment.