"To annul the marriage" means to legally declare that a marriage is null and void, as if it never happened. It is a way to cancel or invalidate a marriage, making it as if the marriage never took place. Full definition
Phil McGraw; Phil McGraw During the process of annulling the marriage in 1973, McGraw began dating Robin Jo Jameson (born December 28, 1953), (myintimcity.com)
Under the Gender Recognition Act 2004, transgender people who are married have been required to divorce or annul their marriage in order for them to be issued with a GRC. (en.wikipedia.org)
Courts will not annul the marriage of spouses who agree not to live together. (divorcesource.com)