adverb, noun which may take the genitive case particle 'no'
to that extent; so much; that much
Expresses a high degree or extent, often with a nuance of surprise or emphasis. Used adverbially or adjectivally with の.
あれほど練習したのに、試合に負けてしまった。
Even though I practiced that much, I lost the match.
あれほど
With that much talent, he will probably succeed.
Refers to 'this extent' (close to the speaker), while あれほど refers to 'that extent' (distant from both speaker and listener).
Refers to 'that extent' (close to the listener), while あれほど refers to a more distant or shared reference.
Compound of あれ (that, distal demonstrative) and ほど (extent, degree).