I don't know if this is how your bird got that comb but if you mix a V-comb with a single comb you will get one of those combs that is straight in the front but splits in the back. Almost all my mixed Polish have them.
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My Polish/serama crossed roo has a comb like that, but my Polish/serama hen has a complete single comb. What breed (or breeds) is the rooster in question?