Crow and Armstrong have been together for over two years

A joint statement gave no reason for the "very tough decision", and they appealed for privacy "at this very difficult time".

Armstrong, 34, who has won the Tour de France a record seven times, has been married once before.

He and Crow, 43, have been together for more than two years.

"After much thought and consideration we have made a very tough decision to split up," the statement read.

"We both have a deep love and respect for each other and we ask that everyone respect our privacy during this very difficult time."

Crow met Armstrong, a testicular cancer survivor who has three children from his first marriage, at a charity event in October 2003.

Grammy award-winner Crow released her fifth album, Wildflower, last September and said that Armstrong had been the inspiration for it.

She performed a free concert in Austin, Texas, Armstrong's home town, to mark the ninth anniversary of his cancer diagnosis.