"And I was like: 'Oh. That girl's getting a lot of laughs, a lot easier than me. What is it?' Because I don't think there's much difference in talent," she told the Telegraph in the UK.
"And I remember distinctly thinking: 'I think it's because she's fatter'. And then, I don't know if it was mega-conscious, but I thought: 'How can I get more laughs? Maybe if I was a bit fatter ...' And then suddenly I was fatter, and doing comedy."
Wilson's Pitch Perfect co-stars Astin and Camp met on the set of the first film in 2013 and got engaged in January of this year during a Hawaiian getaway.
The loved-up couple have made no secret of their affections, raving about each other in a joint interview with PopSugar in June:
"I really do fall in love with her more every day. I always have these moments where I look at her and I feel like I was when I was a child. Is that weird?" said Astin.
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"I feel like he is one of the first people I've ever met, and been with, that has really heard me and seen me and listened," said Camp. "And that's incredibly important."
Wilson shared a picture of the happy newlyweds on her own Instagram page, writing: "Massive congratulations to Sky & Anna. What an absolutely beautiful wedding."