Cem Sultan (also spelled Djem or Jem) or Sultan Cem or Şehzade Cem (December 22, 1459 – February 25, 1495, ; ; ; ), was a claimant to the Ottoman throne in the 15th century.

Cem was the third son of Sultan Mehmed II and younger half-brother of Sultan Bayezid II, and thus a half-uncle of Sultan Selim I of Ottoman Empire.

After being defeated by Bayezid, Cem went in exile in Egypt and Europe, under the protection of the Mamluks, the Knights Hospitaller of St. John on the island of Rhodes, and ultimately the Pope.

Early life 
Cem was born on December 22, 1459, in Edirne. His mother was Çiçek Hatun. In accordance with the custom for a Şehzade (prince) Cem was appointed to a provincial governorship of Kastamonu in 1469. In December 1474, Cem replaced his deceased brother Mustafa as governor of Karaman in Konya.

Succession dispute
At the death of Mehmed the Conqueror, on May 3, 1481, Bayezid was the governor of Sivas, Tokat and Amasya, and Cem ruled the provinces of Karaman and Konya. With no designated heir after Mehmed, conflict over succession to the throne erupted between Cem and Bayezid.

Contrary to Islamic law, which prohibits any unnecessary delay in burial, Mehmed II's body was transported to Constantinople, where it lay three days. His grand vizier Karamanlı Mehmet Pasha – believing himself to be fulfilling the wishes of the recently deceased Sultan – attempted to arrange a situation whereby the younger son Cem, whose governing seat at Konya was closer than his brother Bayezid's seat at Amasya, would arrive in Constantinople prior to his older sibling and be able to claim the throne.

However, Bayezid had already established a political network of influential pashas (two of whom were his sons-in-law), the janissaries, and those opposed to the policies of Mehmed II and the grand vizier. In spite of Karamanlı Mehmet Pasha's attempts at secrecy, the Sultan's death and the grand vizier's plan were discovered by the Janissary corps, who supported Bayezid over Cem and had been kept out of the capital after the Sultan's death. As a result, the Janissary corps rebelled, entering the capital, and lynched the grand vizier.

After the death of Karamanlı Mehmet Pasha, there was widespread rioting among the janissaries in Constantinople as there was neither a sultan nor a grand vizier to control the developments.  Understanding the danger of the situation, former grand vizier Ishak Pasha took the initiative of beseeching Bayezid to arrive with all due haste. In the meantime, Ishak Pasha took the cautionary measure of proclaiming Bayezid's 11-year-old son, Sehzade (prince) Korkut, as regent until the arrival of his father.

Prince Bayezid arrived at Constantinople on May 21, 1481, and was declared Sultan Bayezid II. Only six days later, Cem captured the city of Inegöl with an army of 4,000. Sultan Bayezid sent his army under the command of vizier Ayas Pasha to kill his brother. On May 28, Cem had defeated Bayezid's army and declared himself Sultan of Anatolia, establishing his capital at Bursa. He proposed to divide the empire between him and his brother, leaving Bayezid the European side. Bayezid furiously rejected the proposal, declared that "between rulers there is no kinship," and marched on to Bursa. The decisive battle between the two contenders to the Ottoman throne took place on June 19, 1481, near the town of Yenişehir. Cem lost and fled with his family to the Mamluk Cairo.

In Cairo 
The Mamlūk sultan Qāʾit Bāy (r. 1468–1496) received Cem with honour in Cairo, and Cem took the opportunity to go on pilgrimage to Mecca, making him the only Ottoman prince to have made the pilgrimage.

In Cairo, Cem received a letter from his brother, offering Cem one million akçes (the Ottoman currency) to stop competing for the throne. Cem rejected the offer, and in the following year he launched a campaign in Anatolia under the support of Kasım Bey (Qāsım Beğ), heir of the ruling house of Karaman, and the sanjek bey of Ankara. On May 27, 1482, Cem besieged Konya but was soon defeated and forced to withdraw to Ankara. He intended to give it all up and return to Cairo but all of the roads to Egypt were under Bayezid's control. Cem then tried to renegotiate with his brother. Bayezid offered him a stipend to live quietly in Jerusalem but refused to divide the empire, prompting Cem to flee to Rhodes on July 29, 1482.

Imprisonment

Knights Hospitaler

Upon arriving at Rhodes, Cem asked the protection of the French captain of Bodrum Castle, Pierre d'Aubusson, grand master of the Knights of St. John, the Latin Catholic order on the island. On July 29, Cem arrived at Rhodes and was received with honor. In return for the overthrow of the new sultan Bayezid, Prince Cem offered perpetual peace between the Ottoman Empire and Christendom if he regained the Ottoman throne. However, Pierre d'Aubusson realized that conflict with Bayezid would be imprudent, so he secretly approached Bayezid, concluded a peace treaty, and then reached a separate agreement on Cem's captivity in March 1483. D'Aubusson promised Bayezid to detain Cem in return for an annual payment of 40,000 ducats for his maintenance.

Therefore, the Knights took the money and betrayed Cem, who thereafter became a well-treated prisoner at Rhodes. Afterwards, Cem was sent to the castle of Pierre d'Aubusson in France.

France 

Cem had reached Nice, at that time in the Duchy of Savoy, on 17 October 1482, en route to Hungary, but the Knights were playing for time. After the agreement about his confinement was finalised, he became a hostage, as well as a potential pawn. Those who hoped to use his name and person to foment turmoil in the Ottoman realm included the Mamlūk sultan Qāʾit Bāy, Matthias Corvinus, king of Hungary, and Pope Innocent VIII. Others, such as the Knights of Saint John, the Venetians, the king of Naples, and Popes Innocent VIII and Alexander VI, viewed his presence in Europe as a deterrent to Ottoman aggression against Christendom and an opportunity for profit. For his part, Bayezid II dispatched ambassadors and spies to the West to assure that his rival was detained indefinitely, and he even attempted to eliminate him through assassination.

Cem spent a year in the Duchy of Savoy. After the death of King Louis XI of France (August 30, 1483), who had refused to accept a Muslim in his lands, the Knights of Saint John transferred him to Limousin (D'Aubusson's birthplace). Cem spent the next five years there, mostly at Bourganeuf. He was well treated, but essentially a captive (a fortified tower was constructed to house him). Bayezid II negotiated both with D'Aubusson, to have Cem returned to Rhodes, and with representatives of the new French monarch, Charles VIII, to have him kept in France. When the king of Hungary and Pope Innocent VIII sought custody of the prince, the Pope prevailed, and Cem arrived in Rome on 13 March 1489.

Rome

Innocent VIII rebuffed overtures from the Mamlūks and prepared to launch a crusade against the Ottomans, but it was postponed when Matthias Corvinus of Hungary died on April 6, 1490. These developments worried Bayezid, who contacted D'Aubusson and also sent Mustafa Bey (later a grand vizier) to Rome, to conclude a secret agreement, in December 1490. The sultan promised not to attack Rhodes, Rome, or Venice, as well as to pay Cem's allowance of 40,000 ducats to the Pope (10,000 of which were earmarked for the Knights of Saint John), in return for the prince's incarceration. Apparently, Cem found life in Rome more pleasant than in France, and he had lost hope of seizing the Ottoman throne, but he wanted to die in a Muslim land. His wish would not be realized.

Pope Innocent VIII unsuccessfully attempted to use Cem to begin a new crusade against the Ottomans. The Pope also tried to convert Cem to Christianity, without success. Cem's presence in Rome was useful nevertheless, because whenever Bayezid intended to launch a military campaign against Christian nations of the Balkans, the Pope would threaten to release his brother.

In exchange for maintaining the custody of Cem, Bayezid paid Innocent VIII 120,000 crowns (at the time, equal to all other