Why is "en" included?

Question

In "la surprise n'en sera que plus grande" why "n'en sera que" rather than "ne sera que"?  The lesson says en can replace the preceding de+phrase but I cannot see de+phrase.

Accepted Answer

Hi P. J.
In this fixed expression 'n'en être que plus' (which means 'to be all the more/ to be even more' ) the 'en' is idiomatic.
I would translate it as -
The surprise will be all the greater because of it.
Bonne Continuation !

Answer

Bonjour P J,"la surprise n'en sera que plus grande"  --> The surprise of it (the promotion) will only be the greater.The en is referring back to the long-awaited promotion.Bonne journéeJim