How can I effectively remove a water stain from my ceiling?

Water from bathroom above the living look leaked on to my living room below creating a water stain on the drywall seam of the popcorn ceiling. The leak has since been fixed and I sprayed two layers of Kilz Upshot on the stain, which is around 1" wide by around 3' long. Subsequently, I rolled on two coats of white latex on the whole ceiling. The stain is now not visible in daylight if you stand underneath it. However, at an angle during daytime a light shadow is visible. At night, when the floor lamp is on, you can clearly see the area where the kilz was sprayed. An associate at a home improvement store has suggested I use a Behr sealer again on this area only and then apply another coat of latex on the affected area. Will this work ? Any suggestions would be welcome.