When can pokemon forget HM Moves in XY?

I tought one of my pokemon Strength to test if I could erase it with another TM. Turns out that no, you still have to do something special to forget HM moves just like prior generations.

How can I forget HM moves in Pokemon X/Y?

When you have access to Dendemille Town, Sycamore will approach you beside a house. That house, which is near the Pokemon Center, is the house where the Move Deleter is. Talk to him and he will delete one of your Pokemon's moves.

The Move Deleter can be found in the house northeast of the Pokemon Center in Dendemille Town along with the Move Relearner. The Deleter is the old man on the left and the Relearner is the old woman on the right.