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The Oscar-winner divorced her husband Jesse James last year after reports of his infidelity hit the headlines, while her "Proposal" co-star Reynolds split from wife Scarlett Johansson last month.
The stars have been spotted spending time together as they both cope with their marriage breakdowns, prompting flurries of rumors suggesting they are more than just friends.
Bullock has now spoken out to silence the gossip for good, telling the "Today" show, "I think there will be a collective sigh [of relief] amongst women across the United States when I say he's not my lover. He's just an amazing friend for 10 years ... but I don't get his loving after dark."