Agustín Jerónimo de Iturbide y Huarte

The imperial family first travelled to Livorno in the Grand Duchy of Tuscany but was eventually forced to leave by the authorities, due to pressure from the Spanish King. The former imperial family then reluctantly moved to the United Kingdom.[12] Here, Agustín attended the prestigious Roman Catholic boarding school Ampleforth College, located in North Yorkshire.[13] Agustín de Iturbide was eventually convinced by conservative political factions to return to Mexico and Don Agustín was left to his studies back in England with some of his siblings.[14] Agustín de Iturbide returned to his homeland with his wife and two children on 14 July 1824,[15][16] but was captured and executed shortly after.[17] On his father's death he became the Titular Mexican Emperor and he would be a claimant to his father's empire for forty years until the Second Mexican Empire was established under Maximilian I of Mexico.

Iturbide completed his education at Ampleforth College and received a letter of recommendation saying that he was "a good son, a good brother and a good patriot who will use his experiences and riches for God and for good".[18]

After just a few years, Don Agustín left the UK and travelled to New Granada (present-day Colombia and Panama) where he eventually met and befriended Simón Bolívar, the military and political leader of Venezuela. Don Agustín was made an Adjutant General under Bolívar.[19][20] When the Mexican foreign minister complained about the presence of the Prince Imperial in South America, Bolívar who wanted only to protect the young and unfortunate prince, replied this: "You must calm your mind to his presence, because he would not compete for his father's throne for a thousand reasons". Don Agustín accompanied Bolívar until his final moments in life and it is described in the official report on the hero's death: "Bolívar leaned on his friend and assistant Iturbide, when he helped him up the stairs to his bedroom just before nightfall".[21] In 1831 the Mexican Congress declared that the banishment decree on the former imperial family had been lifted and the Prince Imperial subsequently returned to his homeland.

On his return to the United Mexican States he started working as a Mexican diplomat. He first served at the Mexican embassy in the United States, a post he would retain until 19 March 1833, and would later be transferred to London where he would be stationed until 1835. He was making only 3,500 pesos a year, but he still maintained the large fortune gathered by his deceased father.[22] He also served as a volunteer in the Papal Zouaves, an infantry force created to protect the Papal States. At the outbreak of the Mexican–American War he decided to participate in the defence of his homeland. During the Battle of Padierna on 19 and 20 August 1847, he took command over the Celaya Regiment and tried to rouse his men with his famous patriotic cry: "With me boys! My father is the father of our independence".

The battle of Padierna during the Mexican-American War.

When the Mexican monarchy was revived as the Second Mexican Empire under Maximilian I of Mexico, Don Agustín gave up his claim to the throne and voluntarily approved of the new emperor; he also approved Maximilian's request to adopt two of the Prince Imperial's nephews, Agustín de Iturbide y Green and Salvador de Iturbide y de Marzán. He remained the head of the former Imperial House of Iturbide. Though Don Agustín de Iturbide y Green was proclaimed the new heir apparent he never received his uncle's title of Prince Imperial; this was due to Don Agustín still being alive.

Don Agustín died on 11 December 1866 in New York City. He had been an important figure in both the imperial monarchies; he was largely overlooked when working for the United Mexican States, but did gain some notoriety while serving under Simón Bolívar. The Prince Imperial was buried in Philadelphia next to his mother. Many members of the former Imperial family House of Iturbide would be buried at the same location. Because he died without ever marrying or fathering any legitimate children, his title of Prince Imperial of Mexico was transferred to Maria Josepha Sophia de Iturbide, the daughter of Don Salvador de Iturbide y de Marzán.

He fathered an illegitimate daughter by Nicolasa Fernández de Pierola, a woman from Arequipa in Peru. The daughter, called Doña Jesusa de Iturbide, would later marry the prominent Peruvian politician Nicolás de Piérola (They were first cousins).[23] The current head to both the former imperial houses and the title of Prince Imperial of Mexico is Count Maximilian von Götzen-Iturbide.[24][25]