The couple, who released a joint statement through Armstrong’s spokesman to PEOPLE, are calling it quits after two years of dating and an engagement that lasted a little over five months.
"After much thought and consideration we have made a very tough decision to split up. We both have a deep love and respect for each other and we ask that everyone respect our privacy during this very difficult time," the statement said.
Rumors of trouble began surfacing around Christmas, but the couple insisted there was no truth to them and that they were moving forward with wedding plans for this spring.
Crow recently tried on wedding gowns, including a Vera Wang with what she said was “a particularly absurd amount of meringue,” for a photo shoot for Allure magazine and told reporters that she would be marrying her cyclist boyfriend in Austin.
Armstrong, 34, a Texan, and Crow, 43, born in Missouri, shared a ranch in Austin and were said to be planning to live there together after their wedding.
Eric Gaillard / Reuters
"I knew pretty quickly that I was totally into him,” Crow told PEOPLE in November.
Armstrong popped the question in Sun Valley, Idaho, in late August in a proposal Crow called “very romantic.”
The marriage would have been Crow's first. Armstrong and wife Kristin divorced in 2003 after five years of marriage; they are parents to son Luke, 6, and twins Isabelle and Grace, 4.