The Chicago actress stunned fans and the media when she wed Chesney on the island of St. John in the Caribbean's Virgin Islands on May 9, 2005, after a whirlwind four-month courtship.
Zellweger filed for an annulment of the marriage just four months later, citing "fraud" as the reason for the couple's split. The annulment was granted the following December.
Speaking for the first time about her failed marriage, Zellweger tells British magazine Now, "There was no alternative but to let it go.
"I made the biggest personal mistake of my life. I felt a fool.
"I was looking for something else. I just needed to put acting aside. I needed to sit still and not to worry about the dresses and the hair and the travel and the interviews.
"I was going through huge life changes at the time. I wanted to stop and be a girl for a while. My marriage came during this time and it was desperately important to me. I don't want anyone to think I didn't take it seriously."
Zellweger admits Chesney did not approve when the actress invited her close friend to stay in their Hamptons, New York, farmhouse soon after their marriage.
She explains, "There was no acceptance of my life or my friends. My friend was pregnant, with her husband and young kid. She was doing up her house for the new baby."
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