A tiny bit similar - it's funny when I first smelled them I though the same as you N_Tesla. Later on, after a few sniffs, I could clearly smell the differences. Apres L'Ondee (cassia, violet, heliotrope, iris, vanilla) and L'Heure Bleue (bergamot, pastry-like florals, lots of spices, Guerlinade) are two of my favorite Guerlains.
BTW, what formulation of LHB are you smelling? EdT, EdP, parfum, EdC?