A more thorough explanation:

A progener is a grandson-in-law. This means that a progener is the husband of someone's granddaughter.

• John is Mary's progener because he is married to Mary's granddaughter, Sarah.
• When Jane's granddaughter, Emily, got married, her husband became Jane's progener.

These examples show that a progener is a specific type of family member - the husband of a granddaughter. It is important to note that a progener is not the same as a son-in-law, who is married to a daughter instead of a granddaughter.