Chris Pratt and Anna Faris were "very competitive" with each other during their relationship.
The Hollywood duo - who have a four-year-old son called Jack together - recently announced they are set to divorce and an insider has claimed their desire to be seen as the funniest in their relationship was one of the reasons behind the shock split.
The source said: "They're very competitive with each other. At parties they compete over who's funniest and get insecure if they're not."
Chris' soaring reputation in the movie industry also played a part in their separation, with the 38-year-old actor having starred in a string of big-budget movies over recent years, including 'Jurassic World' and 'Guardians of the Galaxy'.
The insider told the New York Post newspaper's Page Six column: "When he started getting big roles and losing weight, she wasn't the big star anymore.
"He's also very, very religious, and she's not religious."
Earlier this week, another source claimed that Chris' ever-increasing popularity became a source of tension between the pair.
The insider explained: "Chris became this huge movie star and Anna wasn't getting any big jobs. She was the more famous and sexy one at the start of their relationship and then things took a turn."
Despite this, Chris said in a statement on Facebook that he and Anna still retain a "love for each other".
He wrote: "Anna and I are sad to announce we are legally separating. We tried hard for a long time, and we're really disappointed. Our son has two parents who love him very much and for his sake we want to keep this situation as private as possible moving forward. We still have love for each other, will always cherish our time together and continue to have the deepest respect for one another."