|Alexei Nikolaevich Romanov|
|Singing voice actor(s)||N/A|
Alexei Nikolaevich was the only son of Nicholas II and his wife Alexandra Feodorovna and, by extension, the youngest sibling of Grand Duchesses Olga, Tatiana, Maria, and Anastasia. He is loosely based on the historical figure of the same name.
Alexei shares the same fair skin, auburn hair, thick eyebrows, and light blue Romanov eyes as his sisters Olga, Tatiana, Maria, and Anastasia. A large fringe covers his left eye.
His limited appearances in the film portrayed him as a playful boy who was fond of his elder sister Anastasia.
Alexei, the heir to the Russian throne, was one of five members of the Imperial family who died in the revolution by The Bolsheviks as a consequence of the curse cast by the power-mad sorcerer Grigori Rasputin. He later reappears in the film as a ghost in the ballroom of the Catherine Palace during the Once Upon a December sequence and as a figure in the nightmare concocted by Rasputin to lead Anastasia to her death in the North Sea, though the scheme fails thanks to Dimitri.
- According to the film, Anastasia was eight years old rather than seventeen at the time of the revolution. In addition, the film also states that the revolution occurred in 1916 as opposed to 1917. This implies that Alexei, who was three years younger than Anastasia in real life, died at the age of five instead of 14.
- In the nightmare concocted by Rasputin, Alexei is the first of the Imperial children to appear to Anastasia, beckoning her to play with him. The two siblings shared a close bond in real life.
- In the nightmare concocted by Rasputin, Alexei wears a sailor suit, a common sight in photographs of the historical Alexei.
- At a height of 5'6" (1.68 m), the historical Alexei was much taller than his animated counterpart.
- Although Alexei suffered from a blood disorder called hemophilia in real life, few references to his illness appear in the film, barring a scene in the Once Upon a December sequence in which the Tsarevich and his family approaches Anastasia in the ballroom of the Catherine Palace with a slight limp to his walk.