The "lovestruck" singer then tweeted a photo of his bride-to-be, taken "in London last month."
McNeil produced the 2009 documentary about her future husband, Neil Diamond: Hot August Night NYC. She has also worked on documentaries for Motley Crue, Stone Temple Pilots and the Psychedelic Furs, E! News reports.
Diamond was wed to his high school sweetheart, Jayne Posner, for six years. They had two children together and divorced in 1969. Later that year, the singer married production assistant Marcia Murphey. They also had two children together, but after 26 years of marriage, Diamond and Murphey split in 1995.