when does blair have her baby with chuck
In  the fifth-season Blair reveals to Chuck that she is pregnant with Louis's baby.
Season 5
the fifth-season premiere
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Blair Waldorf [SEP] Season 5
In the fifth-season premiere, Blair continues to plan her wedding, but begins to encounter problems in her relationship with Louis. It is later revealed that she is pregnant. Blair tells Chuck that the child is Louis', and states that part of her wanted Chuck to be the father. Dan becomes Blair's confidante and is shown to be in love with her, though she remains oblivious to his feelings and states that there is nothing more than friendship between them. Though she insists that she is in love with Louis, Blair begins to seek Chuck out as the season progresses. The two eventually declare their love for each other prior to a car accident in her limousine while being chased by paparazzi.