New York, New York - Singer Joe Jonas and actress Sophie Tuner have begun a four-day mediation over custody of their two daughters amid their messy divorce.

People reports that the 34-year-old Jonas Brothers singer and the 27-year-old Game of Thrones star have entered into mediation over the custody and parenting plans for daughters Willa and Delphine.

The mediation follows the couple reaching a temporary custody agreement after Sophie sued her ex for allegedly withholding the kids' passports in order to keep them in New York.

The X-Men star's lawyer Stephen Cullen claimed in court that the Burnin' Up singer is asking for joint custody. "What he was looking for is a 50-50," Cullen said.

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"The parties are both seeing their children, which is what we all want," Cullen added.

The custody trial is being overseen by Judge Katherine Polk Failla, who says that she "echoes concerns about the children."