Helena of Serbia, later known as Maria (1447–1498) was the last Queen of Bosnia and Despoina of Serbia.
She was born as the eldest of three daughters of Lazar Branković, Despot of Serbia, and Helena Palaiologina, daughter of Thomas Palaiologos and granddaughter of Byzantine Emperor John VIII Palaiologos. She was baptized as Helena.
As she had no brothers, her father arranged her to marry Stephen Tomašević, the heir apparent to the Bosnian royal crown. The marriage negotiations were led by King Stephen Thomas and the Dowager Despoina Helena. 12-year-old Maria married Stephen Tomašević on 1 April 1459. Immediately upon marriage, Stephen Tomašević succeeded his father-in-law as Despot of Serbia. After marriage, Jelena was referred to as Maria, a name more acceptable to Roman Catholicism, religion formally adopted by her father-in-law in order to reduce the growing pressure made by both Roman Catholic Church and Eastern Orthodox Church when most Bosnians belonged to a separate church called Bosnian Church.
Her husband's reign in Serbia was short-lived. On 20 June 1459, forces under Sultan Mehmed II managed to capture Smederevo and proceeded to annex the remnants of the Serbian state to their realm. Tomašević and Mary fled to Bosnia, seeking refuge at the court of his father.
On 10 July 1461, Maria's father-in-law died. Tomašević succeeded him as King of Bosnia and Mary became the new Queen, replacing her stepmother-in-law Katherine.
Maria's husband asked the Pope and the Venetians to help him defend his kingdom against the Ottoman invasion. However, none ever reached Bosnia. In 1463, Sultan Mehmed II led an army into the country. The royal city of Bobovac soon fell, leaving Tomašević to retreat to Jajce and later to Ključ. The Bosnian Kingdom was soon conquered by the Ottoman Empire. The King was captured in Ključ, and despite promises to the contrary, brought back to Jajce and beheaded on the nearby field known as Carevo Polje (Tsar's Fields).
According to Fine, Queen Maria, a sixteen-year-old widow, survived by fleeing to the coast of the Adriatic Sea. According to "The Fall of Constantinople 1453" (1965) by Steven Runciman, Mary later joined the harem of an unnamed Turkish general. The "Massarelli manuscript" of the 16th reports that Tomašević and Mary had children. However, none are mentioned by name. Their eventual fates are unknown.
Queen Maria died on an unknown date; some sources claim that she died in 1474, while others assert that she died after 1495. She remains unknown to most people, still being in shadow of her stepmother-in-law, Catherine of St Sava, who is often incorrectly referred to as "the last Queen of Bosnia".