Also in "Petty in Pink", Blair and Dan's secret affair is in danger to be uncovered with Serena sending Charlie (guest star Kaylee DeFer) to go undercover Gossip Girl-style to determine why the twosome are spending so much time together.
With Nate's help, Raina decides to go on a search for her long-lost mother. Meanwhile, Chuck's hopes about his legacy are dashed with the reveal of devastating information from the past.
Blair's love story will get more complicated towards the season 4 finale as she will be caught in a love rectangle involving Dan, the prince and Chuck before she chooses the love of her life.
"Petty in Pink" will air Monday, April 25 at 9/8c on The CW. The last episode of this season will air three weeks later on May 16.
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