Hi Varsha, 

In this case the superlative "le plus" is modifying the verb "admirer", and adverbs have no gender so they always use the masculine form:

Le plus and le moins = the most and the least (superlative of adverbs)

However, if it were modifying a noun then you would agree with the gender:

Le, la, les plus and le, la, les moins = the most and the least (superlatives of adjectives)

Hope that helps!