Looks like Gwen Stefani and Blake Shelton have been making sweet, sweet music together. No, that's not a euphemism.Shelton has been teasing a "big" and "shocking" announcement on Twitter , and, according to People , the news is that he and Gwen Stefani have written a country ballad together. The Voice judges recently confirmed their romantic relationship "It's amazing how good she sounds on a pretty country song," an "industry insider" told the magazine. The source added that the song has yet to be cut, but is about a breakup, something the recently divorced musicians can surely relate to.Shelton is expected to share his big news on Today later this morning. He's told fans the announcement is related to both his "personal" and "professional" lives, in which case a duet with his new girlfriend would certainly fit the bill.Stay tuned for more details, and get ready for Gwen to get her cowgirl on.