New results for a two-loop massless propagator-type Feynman diagram

We consider a two-loop massless propagator-type Feynman diagram with an arbitrary (noninteger) index on the central line. We analytically prove the equality of two well-known results in the literature expressing this diagram in terms of hypergeometric functions ${}_3F_2$ of the respective arguments $-1$ and $1$. We also derive new representations for this diagram, which can be important in practical calculations.