Skeletal mesh animation viewer showing UE4 mannequin instead of custom mesh

I made a skeletal mesh that uses the UE4 default mannequin character. When I double-click on the Sheletal mesh thumbnail of the actor and then I click the Animation tab, the animation player shows the mannequin mesh and not my custom character. So I cannot see the mesh behaviour when animated. Of course in play mode, my character is displayed has expected…
This is strange since in many videos about retargeting, the Animation viewer shows the custom character and not the Mannequin !
Let me know if I miss something…