According to the source, the "Sex and The City" star told the crowd at the Love, Peace and Marriage Equality rally in New York City that she became engaged last month.
Actors Kristen Davis, David Hyde Pierce and Audra McDonald were also scheduled to appear at the event, which was organized by the theater community to support New York Governor David Paterson's proposed bill granting legal equality to same-sex unions, Access has learned.
Cynthia began dating Christine in 2003 after splitting with husband Danny Mozes, with whom she has two children, Samantha and Charles.
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