The 28-year-old fashion designer - who won the fourth season of reality show 'Project Runway' in 2007 and debuted his first collection at New York Fashion Week in 2008 - clashed with the 'Tammy' star when he was asked to design a gown for her to wear for the 2012 Academy Awards because they couldn't agree on a style to suit her curves.
He told the New York Daily News: ''Quite frankly she was quite difficult to work with. She wanted some specific things that I thought would not look good on her body.
''And she was not comfortable with them in the end.''
Christian's revelation comes just weeks after the 43-year-old actress claimed that multiple designers had refused to create a dress for her for the very same ceremony - at which she was nominated in the Best Supporting Actress category for her role in 'Bridesmaids'.
She told Redbook magazine: ''Two Oscars ago, I couldn't find anybody to do a dress for me. I asked five or six designers-very high-level ones who make lots of dresses for people-and they all said no.''
Meanwhile, Melissa is set to launch her own clothing line 'Pearl' after alluding to the possibility of starting up a plus-size range in June.
She said: ''When I go shopping, most of the time I'm disappointed.''
The mother of two - who briefly studied fashion and textiles at Southern Illinois University - teamed up with her friend Daniella Pearl to create the collection after the pair worked together to create her 2011 Emmy Awards gown.
The teaser promises plenty of scares when 'IT' hits theatres later this year.
The late singer's funeral took place, among a small gathering of close family and friends, on Wednesday in London.