The Sun's Royal Editor Duncan Larcombe tells ITV News how Prince Charles has gone from being a PR disaster to a 'trendy, on-message global environmentalist'.
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The incident is not believed to be terror-related, British Transport Police said.
The royal couple have been in the US to mark the 300th anniversary of the foundings of New Orleans and San Antonio.
A small number of people were treated at Southgate Tube station, British Transport Police said.