Prince Charles was a delicate child, and was considered so throughout his early manhood, though in reality his health and bodily powers left little to be desired. The first happy years of his childhood were passed at Sigmaringen and the summer residences of Inzigkofen and Krauchenwies. This peaceful life was broken by a visit in 1846 to his maternal grandmother, the Grand Duchess Stéphanie of Baden. On this occasion Prince Charles attracted the attention and interest of Mme. Hortense Cornu, the intimate friend and confidant of Prince Louis Napoleon—later Napoleon III.
It cannot be said that the young Prince progressed very rapidly in his studies; but though he learned slowly, his memory proved most retentive. His naturally independent and strong character, moreover, prevented him from adopting outside opinions too readily, and this trait he retained in after years. For though as King of Roumania he is ever willing to listen to the opinion of others, the decision invariably remains in his own hands.
An exciting period supervened for the little South German Principality with the year 1848, when the revolutionary wave forced the old Prince to abdicate in favour of his son Prince Charles Anthony. Owing to the action of a "Committee of Public Safety," the Hohenzollern family quitted Sigmaringen on September 27. This the children used to call the "first flight" in contradistinction to the "second," some seven months later. Though Prince Charles Anthony succeeded in gaining the upper hand over the revolutionary movement of '48, the trouble commenced again in 1849 owing to the insurrection in the Grand Duchy of Baden. As soon as order had been completely restored, Prince Charles Anthony carried out his long-cherished plan of transferring the sovereignty of the Hohenzollern Principality to the King of Prussia, and in a farewell speech he declared his sole reason to be "the desire to promote the unity, greatness, and power of the German people." The family settled first at Neisse in Prussian Silesia, then at Düsseldorf, as Prince Charles Anthony was appointed to the command of the Fourteenth Military Division, while Prince Charles Anthony, and later on also his brother Friedrich, were settled with their tutor in Dresden, where Prince Charles spent seven years.
Before joining his parents at Düsseldorf, Prince Charles successfully passed his ensign's examination, though he was entitled as a Prince of the House of Hohenzollern to claim his commission without submitting to this test. As a reward for his success he was permitted to make a tour through Switzerland and Upper Italy before being placed under his previously appointed military governor, Captain von Hagens. This officer was a man in every way fitted to instruct and prepare the young Prince for his career by developing his powers of initiative and independence of action. In accordance with his expressed wish, he was gazetted Second Lieutenant in the Prussian Artillery of the Guard, but was not required to join his corps until his studies were completed. A thorough knowledge of the practical part of his profession was acquired at the fortress of Jülich, followed, after a visit to the celebrated Krupp Works at Essen, by a course of instruction at Berlin.
The betrothal of his sister, Princess Stéphanie, to King Pedro V. of Portugal, in the autumn of 1857, was followed by her marriage by proxy at Berlin on April 29, 1858, whilst another important family event occurred in November of the same year. William, Prince of Prussia (afterwards King William I., who had assumed the regency during the illness of his brother the King, Frederick William IV.), appointed Prince Charles Anthony, of Hohenzollern, to the Presidency of the Prussian Ministry. His son Charles developed the greatest interest in politics, and at that time unconsciously acquired a fund of diplomatic knowledge and experience which was to stand him in good stead in his future career.
In the midst of the gaieties of Berlin the Prince was deeply affected by the melancholy news of the death of his sister Stéphanie on July 17, 1859. Two years later the marriage of his brother Leopold to the Infanta Antoinette of Portugal afforded him a welcome opportunity of visiting the last resting-place of his dearly loved sister near Lisbon. On his return from his journey, Prince Charles requested to be transferred to an Hussar Regiment, as the artillery did not appear at that time to take that place in public estimation to which it was entitled. This application, however, was postponed until his return from a long tour through the South of France, Algiers, Gibraltar, Spain, and Paris. After a short stay at the University of Bonn, Prince Charles again resumed military duty as First Lieutenant in the Second Dragoon Guards stationed at Berlin, where he speedily regained the position he had formerly held in the society of the capital. The Royal Family, especially the Crown Prince, welcomed their South German relative most warmly, and the friendship thus created was subsequently more than equal to the test of time and separation.
A second visit to the Imperial Court of France in 1863, this time at the invitation of Napoleon III., was intended by the latter to culminate in a betrothal to a Princess of his House, but the project fell through, as the proposed conditions did not find favour with the King of Prussia. Prince Charles was forced to content himself with the consolation offered by King William, that he would soon forget the fair lady amidst the scenes of war (in Denmark). As orderly officer to his friend the Crown Prince of Prussia, Prince Charles took part in the siege and assault of the Düppel entrenchments, the capture of Fridericia, and the invasion of Jütland. The experience he gained of war and camp-life during this period was of inestimable benefit to the young soldier, who was afterwards called upon to achieve the independence of Roumania on the battlefields of Bulgaria.
The war of 1864 having come to an end, Prince Charles returned to the somewhat dreary monotony of garrison life in Berlin. This not unnaturally soon gave rise to a feeling of ennui and a consequent longing on his part for more absorbing work than that of mere subordinate military routine. Nothing then indicated, however, that in a short time he would step from such comparative obscurity to the wide field of European politics by the acceptance of a hazardous, though pre-eminently honourable, position of the utmost importance in Eastern Europe—the throne of the United Principalities of Wallachia and Moldavia, which, thanks to his untiring exertions and devotion to duty, are now known as the Kingdom of Roumania.