The Queen spent the night in hospital for tests after dramatically cancelling an historic trip to Northern Ireland marking 100 years since the partition of the island.
Royal doctors ordered Her Majesty, 95, to rest and advised her to miss a trip to the province, sparking speculation about the reason for the eleventh-hour cancellation.
It is understood the trip to an unnamed hospital in London on Wednesday afternoon was expected to be for a short stay for some preliminary investigations,