"She's a wonderful girl. Someone had to do it ... it was a tough gig, but somebody had to do it," he joked. "So many people are angry at me."
A rep for the couple confirmed their engagement in late August.
Krasinski, 29, says he had a feeling it was time to propose this summer after about 10 months of dating.
"So many people say, 'You know when you know,' and it's true," Krasinski said. "It's all true."
Krasinski hit the carpet solo. Where was Blunt, 26?
"She's up in Toronto," he said. "Her film [the romantic drama 'The Young Victoria'] is closing the film festival."
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