Besides reading B-L, Twain was familiar with B-L's plays as staged.  One of
the principal roles of Edwin Booth was Richelieu (the cardinal), and T. was
a fairly close friend of EB--praised him after his death (in 1893) in "About
Play-Acting," corresponded with him a bit (usually asking for free tickets
to see him perform), was an incorporator of Booth's The Players club in NY
(est. in 1888), and stayed there often, writing many letters on Players
stationery.  Twain liked attending the theatre, and so all this is to say
that he knew B-L's writings that way, too.