Heartbroken singer Gwen Stefani surprised fans at her New York City concert Saturday when she unexpectedly premiered a personal new song "Used to Love You" - just two months after her split from husband Gavin Rossdale.

She sang, "I thought I was the best thing that ever happened to you," before adding later, "There were no boundaries, but you just pushed me too far. I guess nobody taught you, nobody taught you how to love."

Stefani and Rossdale, who is the lead singer of English rock band Bush, announced they were getting divorced after nearly 13 years of marriage, citing irreconcilable differences. The couple has three sons together.

The stars in a statement said, "While the two of us have come to the mutual decision that we will no longer be partners in marriage, we remain partners in parenthood and are committed to jointly raising our three sons in a happy and healthy environment."

However, Stefani hasn't let the separation hold back her professional career. In addition to writing her passionate new track, the former No Doubt front woman presently serves as a judge on NBC's highly rated singing competition, "The Voice."