The following is from TMZ.com:

Liz' attorney tells us, Cena blindsided her with the divorce filing. They had been having issues -- and Cena even approached her recently with a pre-divorce financial settlement agreement -- but Liz refused to sign it, convinced the relationship would still work out.

FYI -- It's not uncommon in celeb divorces to bring up pre-divorce settlement agreements because they help simplify otherwise messy splits.