According to the National Gallery online catalogue description, ‘The connections between the family of Mme de Souscarrière and the slave trade may also in part explain the presence of the young black page in the portrait’ (‘Mme de Souscarrière (?) and her Page’, <https://www.nationalgallery.org.uk/paintings/nicolas-de-largillierre-and-studio-mme-de-souscarriere-and-her-page> accessed 5 August 2021.) This needs to be corroborated.
This person is the subject of ongoing research. We have started by researching their relationship to the enslavement of people.
National Gallery painting connections
Sitter: Madame de Souscarrière is the subject of a portrait by Nicolas de Largillierre and his studio, Mme de Souscarrière (?) and her Page (NG3883), bought in 1924.
History of Parliament Trust (ed.), The History of Parliament: British Political, Social & Local History, London 1964-, https://www.historyofparliamentonline.org/
Checked and not found — Item on publisher's website