De or het legendevorming?

The correct Dutch article is:

de legendevorming

Rule Words ending in -ing: almost always de. See the rule

How to use legendevorming

the legendevormingde legendevorming
this legendevormingdeze legendevorming
that legendevormingdie legendevorming
our legendevormingonze legendevorming
your legendevormingjouw legendevorming
every legendevormingelke legendevorming
which legendevorming?welke legendevorming?
a big legendevorming / the big legendevormingeen grote legendevorming, de grote legendevorming