Epic and La Grandes Battles expansions differences

Hi all,
I am new to the system - just preordered base game and most expansions.
I ordered the Epic expansion.
But I fail to see in what it is different from the Grandes Battles: both have Epic and Grandes Battles boards, for an example.
So can one explain me what The Grandes Battles adds to Epic?

Thanks in advance.

Don't know all the particulars, but tentatively, The Grand Battles (Expansion 7) adds 12 EPIC scenarios, 12 Grand Battle scenarios, a mounted Grand Battles board, two extended pre-printed grand battle maps for battles of Borodino and Waterloo, new rules and blocks for leaders of honor (may order more units on a take command card), iconic leader powers (for Napoleon, Wellington, and others), a few rules tweaks, and additional other stuff such as units, terrain, etc.
Note: you will need expansion 5, Generals, Marshals, and Tacticians, to effectively use the EPIC and Grand Battles expansions.

Thank you for the answer.
I find strange that two types of "larger" battles were created...