It is a well-known fact and easy to prove that if Γ and Γ′ be any two class-cubics and P a variable point, such that the pencil of lines from P to Γ apolarly separate the pencil of lines from P to Γ′, then the locus of P is a cubic curve G called the “apolar locus” of Γ and Γ′. Also, Γ and Γ′ are said to be co-apolar class-cubics” of G, or simply “co-apolars” of G. The problem of finding the general system of co-apolars of a given cubic curve has not yet been completely solved, but particular and more important cases have been investigated by me in several papers contributed to the London Mathematical Society. In the present communication I propose to deal with the most general solution of the above problem.