Originally Posted by
cafeconleche
Returning, show the gate agent the DE passport, and if/when asked about ESTA, say you're a US citizen too, and if asked about the passport, show it. Again, shouldn't be a problem. Chinese immigration likely only need your DE passport. Again, if asked...
One note on the ESTA: this i checked at checkin, i.e. also at online check-in. If the airline does not have the information about the US passport, you won't be able to do online check-in and you will have to do it at the airport.