At birth, Victoria was fifth in the line of succession after her father and his three older brothers: the Prince Regent, the Duke of York, and the Duke of Clarence (later William IV). The Prince Regent and the Duke of York were estranged from their wives, who were both past child-bearing age, so the two eldest brothers were unlikely to have any further children. The Dukes of Kent and Clarence married on the same day 12 months before Victoria's birth, but both of Clarence's daughters (born in 1819 and 1820 respectively) died as infants. Victoria's grandfather and father died in 1820, within a week of each other, and the Duke of York died in 1827. On the death of her uncle George IV in 1830, Victoria became heiress presumptive to her next surviving uncle, William IV. The Regency Act 1830 made special provision for the Duchess of Kent to act as regent in case William died while Victoria was still a minor. King William distrusted the Duchess's capacity to be regent, and in 1836 declared in her presence that he wanted to live until Victoria's 18th birthday, so that a regency could be avoided.
What happened when Victoria's Uncle George IV died?
became heiress presumptive to her next surviving uncle