Replacing cracked shower wall tiles and found a 1 inch groove in the concrete base around the outside edge...?

Question:Found a 1 inch deep groove about 1/8 inch wide all around the base of the shower. The bottom row of wall tiles slid down into this groove and then butted up against the floor concrete/tiles. I'm guessing the seal failed between these bottom tiles and the floor allowing water into the groove and cracking the tiles.

Has anyone heard of this? Should I slide the new tiles back into the groove (kinda tricky) and reseal? Or should I fill the concrete groove with something, trim the bottom tiles and just place them on the wall over the new wider base? If I fill the groove, what substance should I use... would it need to allow for expansion?

Answers:
try filling the groove with grout?