Alexei Antonovich of Brunswick-Lüneburg (27 February 1746 – 12 (23) October 1787), was the third son of Duke Anthony Ulrich of Brunswick and Grand Duchess Anna Leopoldovna of Russia, and younger brother of Ivan VI.

In contrast to that of their elder brother, the deposed Ivan VI, who was placed in solitary confinement, the younger siblings were kept together with their father after the death of their mother in 1746.

In 1780, Empress Catherine was arranging for their release and transfer to the custody of their paternal aunt, the Danish queen dowager Juliana Maria of Brunswick-Wolfenbüttel in Denmark.

While being physically weak, however, all four siblings were described as intelligent, likable and humane people, who had learned to read and write on their own despite the prohibition of the Imperial decree.

They reportedly had a friendly relationship with each other, spending their days tending to the garden and their hens and ducks, riding, chasing each other on the frozen lake at winter, and playing chess and cards.

While leaving Russia by ship on the 27 June 1780, the siblings reportedly started to cry upon seeing the fortress in Arhangelsk, believing that they had been tricked and would be separated and each placed in solitary confinement.