J. Lucas-Dubreton
The Fourth Musketeer: The Life of Alexander Dumas
Translated From the French By Maida Castelhun Darnton
The Fourth Musketeer is an English translation of a French biography of Dumas called “La Vie d’Alexandre Dumas Père” (1928)
I found the biography at this Dumas site:
http://www.cadytech.com/dumas/