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Heidi Montag's father has been arrested in Colorado on charges of incest and child sex abuse of a 13-year-old girl.

Bill Montag was arrested on Jan. 29 and authorities are alleging that the crimes have been going on for years.

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According to court documents obtained by TMZ, Bill allegedly abused the girl at least 50 times during a span of 1993-1997 when the girl was between 13 and 17 years old.

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The graphic documents state that Heidi's dad "groomed her with back rubs in her bedroom in the basement of their home." Eventually the acts escalated and he began performing oral sex on the girl when she was 16.

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There is no indication that Bill abused either of his daughters, Heidi or Holly. The victim has not been named.