The WAG is marrying Manchester Utd footballer Wayne Rooney, 22, on 12 June.
Coleen, 21, will be wearing a £100k Marchesa strapless gown for the ceremony on the Côte D'Azur.
The extravagant dress has a 25ft train, which will be studded with Swarovski crystals.
'Coleen's going to look like Cinderella,' a source tells the Daily Star. 'It couldn't be more appropriate as she has planned a fairytale wedding with Wayne.'
The frock has been designed by Marchesa's Georgina Chapman.
She flew in from New York to meet Coleen for the fitting at the Baglioni Hotel.
'She arrived with two massive boxes, one for the dress and one for the train,' adds the source. 'It took four guys to carry a single box.'
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