Court rumour attributed María Isabel's paternity not to the king, but to the young Godoy, who became Spain's prime minister in 1792.

[6] Napoleon had a low opinion of the House of Bourbon and commented privately, "If I would have to remarry, I wouldn't look in a house in ruins for my descendants"[6] Anxious to find a crown for Maria Isabel, in the spring 1801, her mother looked to marry her to her paternal first cousin the Duke of Calabria, Prince Francesco of Naples and Sicily, whose wife, Archduchess Maria Clementina of Austria, was then still alive, but died of consumption in November of that year.

[6] His plan was to bring the Kingdom of Naples, an ally of England and hostile to France, into the recently formed Spanish-French alliance, proposing a closer relationship between the two families through double marriages.

The Queen, Maria Carolina of Austria, who hated France and mistrusted Spain for its good will toward Napoleon, opposed the match.

[6] Infanta Maria Isabel was only twelve years old; even at a time when princesses married very young, her tender age was unusual for a bride.

But her early marriage was justified by the need to secure the hasty resumption of close relations between Spain and Naples at a particularly critical time for the European courts, struggling with the expansionist policy of Napoleon.

[7] The festivities lasted until 12 October when María Isabel, in Italian Maria Isabella, left Barcelona towards Naples.

[8] María Isabel had regular features and was relatively better-looking compared to Carlota Joaquina and Maria Amalia, but she looked even younger than her thirteen years.

She had an unfavorable first impression of the young María Isabella, about whom she wrote: A fine, fresh, healthy face, not Bourbon in the least, but white and red, with black eyes.

All the numerous Spanish clique, all their projects and schemes, have received a knock out blow by the arrival of this Princess and her perfect nullity.

Napoleon's troops defeated the allied armies at the Battle of Austerlitz in December 1805 and the Neapolitan corps at Campo Tenese.

[10] Despite successive attempts by Murat to invade the island, King Ferdinand and Maria Carolina held their status and power in Sicily under the protection of British troops, but would be unable to challenge French control of the Italian mainland.

Francesco clashed with the aristocracy of the island who opposed new taxes to finance the war against France, claiming a high degree of autonomy.

[11] Maria Isabella was instrumental in the marital choices of the Neapolitan court for her daughters, of whom four (out of six) married members of the Spanish royal family.

The first of these marriages took place in April 1819 between her eldest child Luisa Carlotta and Maria Isabella's younger brother, Infante Francisco de Paula of Spain in a union between niece and uncle.

[5] From the beginning, Francis I behaved very differently from the liberal prince he had been as heir to the crown and his short reign was essentially reactionary.

[5] The king's valet, Michelangelo Viglia, and Caterina de Simone, the Queen's lady-in-waiting, ruled the royal household in which corruption was rampant.

[10] Their security was guaranteed by the Austrian troops stationed in Naples, but their expenses were a heavy burden on the state coffers and the main reason for the high public debt.

[10] On Medici's advise, Francis and Maria Isabella, taking with them their one-year-old son the Count of Aquila, went to Milan in May 1825 in order to obtain a reduction in the occupation troops.

[10] After an agreement between Medici and the Austrian ambassador Count Karl Ludwig von Ficquelmont, the King and Queen returned to Naples on 18 July.

Maria Isabella's eldest daughter, now Infanta Luisa Carlota, quickly arranged the marriage between her sister and their uncle.

Francis I's was afflicted with gout and on declining health, but Maria Isabella was anxious to visit her native country after 27 years of absence.

Unbeknownst to her, she was at the center of a liberal conspiracy hatched by Prince Vincenzo Ruffo della Scaletta and Peter Ugo, Marquis delle Favare.

Their intention was to name Maria Isabella regent, displacing her conservative son from the throne for at least a couple of years.

[5] When the ambitious baron claimed the style and privileges of Royal Highness as a condition for marrying her, Maria Isabella rejected him, appealing to her son to rid her of her former lover.

As Maria Isabella was determined to remarry, her son, King Ferdinand II, gave her a list with names of young noblemen of the kingdom, from whom to choose.

Ultimately she selected Francesco, Count dal Balzo dei Duchi di Presenzano (1805–1882), a handsome young lieutenant from an ancient but impoverished noble family.

In 1845, to keep the Spanish throne in the House of Bourbon Louis Philippe d'Orléans, King of the French, launched the idea of marrying Maria Isabella's youngest son Francesco, Count of Trapani, who had been originally destined for the church, to Queen Isabella II of Spain, her granddaughter, in another union between uncle and niece.

Due to her affable character and generosity towards the poor, Maria Isabella remained a popular figure till the end.