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Here's what wikipedia says

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, she became heiress presumptive to her next surviving uncle, William IV. The Regency Act 1830 made special provision for Victoria's mother, the Duchess of Kent, to act as regent in case William died while Victoria was still a minor.[5] 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.[6]