Kings that are the first to use a name don't usually have the number I.
Victoria is not Victoria I unless there will be a Victoria II.
In the doubtful case that Leonor's first born would be named Francisco, would he be styled Francisco I or the II ?
In Portugal, the two King Consortes D.Pedro, D.Maria I's husband and D.Fernando, D.Naria II's husband, both had a regal number - D.Pedro III and D.Fernando II.
As there has never been a king Francisco in Spain, before or after king Francisco de Assis, would he be considered Francisco I in case of a future namesake ?