Alexander has said in his post concerning a "clean line", the "DNA test should prove a match"; however, the "match" may be a bit wobbly at the 8 generations removed distance; not because of any skullduggery, but because it only takes a very few generations for small differences to begin to appear in the Y-DNA profile, even of closely-related cousins.
For instance, the name "Brown" in Scotland is the second most common surname, being only exceeded by "Smith". In the Family Tree DNA Project for the surname "Brown", there are presently 153 separate subgroups of DNA profiles on the first 67 loci (places on the tiny Y-chromosome) that are covered in the common Y-DNA test (and there are many more "Brown" surnamed men who have tested, but have not yet been able to be placed in one of those subgroups). In one of those subgroups, there are two known third cousins, once removed, who have a valid paper trail of their ancestry back 8 generations. The great-grandfather of one cousin was the younger brother of the 2-great-grandfather of the other one. Since one of the cousins has only been tested for the first 37 of those 67 loci, they can only be compared on those first 37 loci.
Now of those first 37 loci (or places on the Y-chromosome) that were inherited directly down the male line of both cousins, there are 14 of the 37 loci that have been classified as "fast mutators" - for every male; not just for those surnamed "Brown".

That means that minor changes at one or more of those 14 tested places occurs at a significantly faster rate than the remaining 23/37 places on the Y-chromosome. As a result, the cousins have a Y-DNA "match", but they have a VERY slight difference at one of the 37 tested spots on their personal Y-chromosomes and the difference has occurred (as expected) at one of those 14 known "fast mutator" loci in only four generations.
So, given the fact that there are a number of known "fast mutator" loci on every human male Y-chromosome, and that small changes are known to occur relatively rapidly at those places; at an 8-generation distance, Alexander's "match" could easily have three or four small different Y-chromosome values and still be considered a "match" - without any "non-paternal event" having occurred.

The values do not have to be exactly identical to be considered a "match".