Article: Life with My Sister Madonna, a book by Madonna's brother Christopher, debuted at number two on The New York Times bestseller list. The book caused some friction between Madonna and her brother, because of the unsolicited publication. Problems also arose between Madonna and Ritchie, with the media reporting that they were on the verge of separation. Ultimately, Madonna filed for divorce from Ritchie, citing irreconcilable differences, which was finalized in December 2008. She decided to adopt from Malawi. The country's High Court initially approved the adoption of Chifundo "Mercy" James; however, the application was rejected because Madonna was not a resident of the country. Madonna appealed, and on June 12, 2009, the Supreme Court of Malawi granted Madonna the right to adopt Mercy James. She also released Celebration, her third greatest-hits album and final release with Warner. It contained the new songs "Celebration" and "Revolver" along with 34 hits spanning her career. Celebration reached number one in the UK, tying her with Elvis Presley as the solo act with most number one albums in the British chart history. She appeared at the 2009 MTV Video Music Awards on September 13, 2009, to speak in tribute to deceased pop star Michael Jackson.

Question: When was the divorce finalized between Madonna and Ritchie?
December 2008