In this talk, we will show a connection between one of the three integrable cases of the cubic Hénon-Heiles Hamiltonian system and the KdV with one source system.In the system made of KdV with one source, we first show by applying the Painlevé test that the two components of the source mnust have the same potential.Then, we show how the computation of the Lax pair naturally introduces an additional term proportional to the inverse of the squared eigenfunction.This allows us to prove the identity between the travelling wave reduction and one of the three integrable cases of the cubic Hénon-Heiles Hamiltonian system.