After the possible discovery of a monochromatic gamma-ray line around 3.55 keV, a myriad of models where proposed to interpret it as a decaying dark matter candidate. I will in this talk introduce the experimental results, mentioning recent discussions about the validity of the result. Then I will present our recent work in collaboration with Emilian Dudas and Yann Mambrini, in which we propose a different scenario where a keV dark matter annihilates to produce such a monochromatic signal. The process is generated through the exchange of a light scalar of mass of order 300 keV - 50 MeV coupling to photon through loops or higher dimensional operators. For natural values of the couplings and scales, the model can generate a gamma-ray line which can fit with the recently identified 3.5 keV X-ray line.