LOS ANGELES, Oct. 1 -- Nicole Kidman has officially filed for divorce from Keith Urban, ending a nearly two-decade marriage that had long been considered one of Hollywood's most enduring unions.

The Oscar-winning actress, 57, made the filing in Tennessee on Tuesday, citing "irreconcilable differences," the BBC reported today.

Kidman and Urban, also 57, have been married since June 2006 and share two daughters: Sunday Rose, 17, and Faith Margaret, 14.

A source told gossip siteTMZ that the couple, who had been living apart since the summer, were already on separate paths - and that while Urban was ready to move forward, "Nicole did not want to split."

The filing comes as a shock to fans who have watched the pair navigate both triumphs a...