Victoria turned 18 on 24 May 1837, and a regency was avoided. On 20 June 1837, William IV died at the age of 71, and Victoria became Queen of the United Kingdom. In her diary she wrote, "I was awoke at 6 o'clock by Mamma, who told me the Archbishop of Canterbury and Lord Conyngham were here and wished to see me. I got out of bed and went into my sitting-room (only in my dressing gown) and alone, and saw them. Lord Conyngham then acquainted me that my poor Uncle, the King, was no more, and had expired at 12 minutes past 2 this morning, and consequently that I am Queen." Official documents prepared on the first day of her reign described her as Alexandrina Victoria, but the first name was withdrawn at her own wish and not used again.
When did Victoria become Queen upon William IV's death? 
20 June 1837