HSH Princess Gabriella was the heiress presumptive to Monaco's throne for only four minutes on the 10th of December, 2014.

False:

HSH Princess Gabriella was the heiress presumptive to Monaco's throne for only two minutes - the amount of time that passed between her birth and the birth of her twin brother, Hereditary Prince Jacques of Monaco, Marquis de Baux. Under the constitution of Monaco, the crown passes according to male-preference cognatic primogeniture.

Gabriella is the elder child and only daughter of the reigning Prince of Monaco, Albert II, and his wife, HSH The Princess of Monaco. She and her brother were born at Monaco's Princess Grace Hospital on the 10th of December, 2014.

They have two older half-siblings, but as Albert was never married to either of their mothers, neither is eligible to inherit the Monegasque throne. (Monaco's Civil Code 229 states: "Les enfants légitimés par le mariage subséquent auront les mêmes droits que s'ils étaient nés de ce mariage"). The line of succession was most recently and notably modified by a constitutional change implemented by Princely Law 1.249 of 2 April 2002.