Guess hell has frozen over.

Blair Waldorf (Leighton Meester) and Dan Humphrey (Penn Badgley) struck up an unexpectedly flirty friendship on season four of Gossip Girl -- but Brooklynite Humphrey's growing romantic feelings for Blair were thwarted by both her undying love for Chuck Bass (Ed Westwick) and an engagement to Monaco royal Prince Louis (Hugo Becker).

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But, shooting scenes for the CW hit in NYC on Monday, Meester (in a dramatic pink gown) and Humphrey were photographed in a passionate kiss.

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On the landmark 100th episode which aired Jan. 30, Dan provided the getaway car for Blair after her disastrous wedding to Prince Louis (who angrily vowed they'd have a loveless, obligatory marriage after she was discovered speaking romantically with Chuck).

No word yet on whether the lip-lock -- the unlikely pair have yet to kiss -- was perhaps part of a dream sequence or the real deal.

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Tell Us: Should Dan and Blair get together, already?

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