In certain countries, such as the United States and Canada, first-to-use trademark systems are in place. This means that trademark rights are given to marks that have been used in commerce the longest, granting priority in the jurisdiction of use to which you would like to apply. It is important to note that registering a trademark as the first applicant does not guarantee priority due to this first-to-use rule.
In the United States, rights to a mark are established by actual use of the designation rather than registration. Therefore, the rule is that ownership of a mark is given to the first-to-use, not the first-to-file. If you are the first to use a trademark in multi-state commerce, you may have priority over those who use the same trademark later. This could potentially make you the rightful owner of the mark.
Although, you would be requested to provide evidence to support your claim that you have been using the brand in multi-state commerce prior to the third party's registration.