[Las Vegas Ron]

Seems to me it would be like a fraudulent preacher marrying a man and a woman.

After the fraud was discovered, the marriage would become null and void.

Just my $.02

[little jeremiah]

Or if a man or woman already legally married marries another spouse, the subsequent marriage is null and void.

[Terabitten]

Seems to me it would be like a fraudulent preacher marrying a man and a woman. After the fraud was discovered, the marriage would become null and void.

Off topic, but the marriage would still be legal if the man and woman married in good faith, believing the preacher to be qualified/certified to perform the ceremony.

The example you're looking for is a man who is married to one woman who marries another woman without telling her about his first wife. Because he did not act in good faith, the marriage would be void.