Linq: Except on two different types of dictionaries

i have 2 different types of dictionaries Dictionary<int, Fooclass> oldDic and Dictionary<int, string> barList newDic . Now i need to compare values in both dictionaries. for Example key can be in

• oldDic : 1,2,3
• newDic : 1,2,3,4
• Expected Output : 4

Now i need to compare both dictionaries on basis of their keys any help would be appreciated.

Edit : Output should be like second dictionary(newDic) but this will contain some value of 2nd dictionary's(oldDic). For example

1,"fooString" Where fooString is some value in Fooclass's someproperty.... For more clarity see this which doesn't worked for me

var addedList = from list1 in baseListDic
join list2 in trackerlist on list1.Key equals list2.Key
 select new { key = list1.Key, value = list1.Value._lead };

here baseListDic is oldDic and trackerlist is newDic.... Let me know if i'm still not clear...