The late Queen Elizabeth 's brutal response to being told her only sister, Princess Margaret, was threatening to take her own life amid a mental breakdown over her marriage ending has been uncovered, RadarOnline.com can reveal.

While the monarch was poised and reserved in public, her "cool and dry humor" was apparently free-flowing when she was out of the spotlight.

Royal biographer Andrew Morton detailed one particularly harsh moment the late Elizabeth's dark humor was on display in 1974 when she received a frantic call about Margaret's well-being. Article continues below advertisement

Margaret Breaks Down as Marriage Falls Apart in 1974

At the time, Margaret's marriage to Antony Armstrong-Jones, 1st Earl of Snowdon, was falling apart. Margaret met her future husband at a din

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