Compare string patterns and exclude characters that are not common C#

I have two string A = ABCDEFG, string B = ABCDHJKL and string C = ABC. I want to compare the strings and get only the maximum matching part of and non-matchng part as separate strings. For example, in the above example the result should be ABCD is matching and non-matching is EFGHJKL.

Is there a way we can do this using string manipulation or using Tries is the only way out?