I am trying to learn the conjugation of French verbs. It is straight easy for the first and the second groups with verbs ending with -er and -ir respectively. However, I got confused when I tried to solve exercises with some verbs (from the first group), where the consonant letter is sometimes duplicated:
For example: The verb Feuilleter:
So why is the t duplicated for je, tu, il, and ils? Is this related to the pronunciation of the word? Are there any verbs in the second group (-ir) with the same property?