3 books in series

The d'Artagnan Romances

The d'Artagnan Romances is a 7-book series with 3 released primary works first released in 1844 with contributions by Alexandre Dumas.

I tre moschettieri
The Red Sphinx
Twenty Years After (The D'Artagnan Romances #2)
Le Vicomte de Bragelonne
Ten Years Later
Louise de la Valliere
The Man in the Iron Mask