raster - Opening .grd from R in QGIS?

How to open .grd raster layers in QGIS (or any other GIS)?

I have looked through previous questions, but not found any answer. My raster layers are outputs from running bfastSpatial in R and I can't seem to open them in QGIS. I have also been unsuccessful in converting the format to .tif so I am hoping there is some other option.