New laws needed to allow Spain's King Juan Carlos to abdicate in favour of his son have been set in train by the Spanish parliament.
The country is due to have his son, Crown Prince Felipe, crowned as King on the throne within three weeks.
But with slipping ratings and a corruption scandal stubbornly swirling around the family, the esteem of the monarch is being eroded fast, as Correspondent Dan Rivers reports.
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The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
A man, apparently armed with a small axe and a large stick, was detained close to the event and police cleared the area as a precaution.