This was the case with the sketches for the first three parts of the tetralogy.
From the en.wikipedia.org
It is this magnificent tetralogy of novels that I now regard as Mann's finest work.
From the guardian.co.uk
Has cinema ever seen a more tedious tetralogy than Pirates of the Caribbean?
From the telegraph.co.uk
Enough loose ends still hang at the close to suggest a possible tetralogy.
From the independent.co.uk
Nevertheless, Wagner always referred to the Ring as a trilogy rather than a tetralogy.
From the en.wikipedia.org
Yukio Mishima completed his tetralogy, The Sea of Fertility, one November morning in 1970.
From the time.com
When a trilogy turns into a tetralogy, it is because the grudge remains.
From the latimes.com
The film is the first in a tetralogy directed by Romero and spawned four unofficial sequels.
From the en.wikipedia.org
In 2001, Tom Markus directed an adaptation of the tetralogy at the Colorado Shakespeare Festival.
From the en.wikipedia.org
More examples
A series of four related works (plays or operas or novels)
A tetralogy is a compound work that is made up of four (numerical prefix '''') distinct works, just as a trilogy is made up of three works.
(1) In a general sense, a collection of four narratives that are contiguous and continuous in chronology. Just as three books that tell a continuous story constitute a trilogy, four books that tell a continuous narrative are a tetralogy. ...
Greek tetra = four, and logos = discourse, hence a combination of four elements e.g., symptoms or defects.
Used to describe a common heart defect with four components (Fallot's Tetralogy).
Group of four plays presented by a tragic playwright at the City Dionysia, composed of three tragedies and a satyr play. ...
A grouping of four plays by theme and content; in the ancient Greek theater the tetralogy customarily comprised three tragedies (a trilogy) and a satyr play. ...
Four works constituting a group. Thus, Shakespeare's CHRONICLE PLAYS Richard II, Henry IV, Parts I and II, and Henry V constitute a tetralogy. Greek drama was presented in tetralogies, consisting of three tragedies followed by a SATYR PLAY. ...