The Hillscouple Heidi Montagand Spencer Pratthave accused each other of being unfaithful, following the supposed break-down of their marriage.
According to RadarOnline, Heidi has allegedly hired a private investigator to spy on her estranged hubby to find out whether he has been cheating on her.

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A source revealed: "She is very anxious to find out if her suspicions and the rumours are true, especially if he’s spent any money on another woman,”
Montag is said to have hired a former sheriff to look into Pratt's private life as the insider added: “It is really important to Heidi to find out if Spencer has been cheating on her.”
Meanwhile, Spencer has also accused his 23-year old surgically enhanced ex of cheating on him, claiming that Heidi was unfaithful with his former BFF and bodyguard, Cougar Zank.

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Montag and Cougar reportedly travelled to New York together for a shopping trip and Heidi is also staying in Zank's Malibu home with Hills co-star Jennifer Bunney.

As we previously reported, Speidi are said to have blown their earnings from being reality TV stars leaving them 'completely broke' and have staged the split for publicity.
Heidi is also allegedly living in fear that she could be pregnant with Spencer's baby after having a healthy sex-life right up until she walked out on Pratt.