Princes William, Edward, Andrew fly to ailing Queen

STORY: They are heading to Balmoral Castle, around an hour's drive away from Aberdeen Airport where they landed.

The queen, Britain's longest-reigning sovereign and the world's oldest monarch, has been suffering from what Buckingham Palace has called "episodic mobility problems" since the end of last year.

"Following further evaluation this morning, the Queen's doctors are concerned for Her Majesty's health and have recommended she remain under medical supervision," the palace said in a statement.