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ex-, former, then

Hyphenate ex- as a prefix when it means former:
            ex-Governor Patricia B. Kellogg
            ex-farmer

However, former is preferable, especially when space permits:
            former President Ronald Reagan
            the former first lady

Do not use former when reference is made to something done while a person held a position; then may be used:
            then Chief Justice Warren E. Burger or simply, Chief Justice Warren E. Burger

No hyphen in compounds unless ambiguous:
            then photographer Chris Johns

See late, latter, former.