Just four months after his headline-making nuptials to actress Nicole Kidman, country music superstar Keith Urban has checked himself into rehab. ‘I deeply regret the hurt this has caused Nicole and the ones that I love and support me, Urban explains in a statement released to OK!. ‘One can never let one’s guard down on recovery and I’m afraid I have. With the strength and unwavering support I am blessed to have from my wife, family and friends, I am determined and resolved to a positive outcome.’ Keith had Nicole by his side when he admitted himself into a treatment center on the evening of October 19. The New Zealand-born singer had admitted to free-basing cocaine in the past, telling USA Today, ‘I had this house in Nashville where I used to do drugs.’ He later checked himself into Cumberland Heights, a Nashville treatment center. It is not yet known if he returned to the same facility.Keith had been scheduled to receive a star at the Walk of Fame at Connecticut’s Mohegan Sun Hotel & Casino on Oct 20. That ceremony plus all scheduled appearances for his upcoming CD, titled Love, Pain & the Whole Crazy Thing, have been put on hold.