Based on the English alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Whic…

Based on the English alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Which letter-cluster DOES NOT belong to that group? (Note: The odd one out is not based on the number of consonants/vowels or their position in the letter-cluster.)