Complex sentence: No definite primary evidence has yet come to light that effectively dispels the secrecy that Leighton built up around himself, although it's clear that he did court a circle of younger men around his artistic studio.
Split into simpler sentences: No definite primary evidence has yet come to light that effectively dispels the secrecy that Leighton built up around himself. Although it's clear that he did court a circle of younger men around his artistic studio.