  A Galton-Watson process in varying environment is a discrete time branching
process where the offspring distributions vary among generations. Based on a
two-spine decomposition technique, we provide a probabilistic argument of a
Yaglom-type limit for this family processes. The result states that, in the
critical case, a suitable normalisation of the process conditioned on
non-extinction converges in distribution to an exponential random variable.
Recently, this result has been established by Kersting [{\it J. Appl. Probab.}
{\bf57}(1), 196--220, 2020] using analytic techniques.
