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Charmed, season 4 episode 15 «Marry-Go-Round»: air date March 14, 2002. Episode overview, season trailer and the cast of Charmed.
When the Seer has a vision that Cole and Phoebe's son will be the most powerful being to live, she informs the Source of this. As a result, Cole begins to sabotage Phoebe's plans of having a white wedding, so they can get married in a dark ceremony.