Former White House chief of staff Reince Priebus was interviewed by special counsel Robert Mueller's team on Friday, according to his lawyer, William Burck. “Mr. Priebus was voluntarily interviewed by Special Counsel Mueller’s team today. He was happy to answer all of their questions," Burck said.The interview was expected as part of Mueller's sprawling Russia-related investigation, and Priebus had been preparing for several weeks, according to people who spoke with him.Priebus didn't immediately return a request for comment Friday afternoon.