MONDAY, MARCH 23

"GOSSIP GIRL" � (8:00-9:00 p.m. ET)

"The Grandfather" (CONTENT RATING TBD) (HDTV)

BLAIR WALDORF EXPLORES HER DARK SIDE � Devastated by the recent plot twist in her life, Blair (Leighton Meester) turns her back on her predictable Waldorf existence in favor of a more wild and unpredictable lifestyle, causing Serena (Blake Lively) and Chuck (Ed Westwick) to have serious concerns about their friend. Vanessa (Jessica Szohr) convinces Nate (Chace Crawford) that it may be time to forgive and forget when it comes to his mother's Kennedyesque family, The Vanderbilts, who abandoned Nate and his mother when they needed them most. In a misguided effort to be completely honest with each other, Lily (Kelly Rutherford) and Rufus (Matthew Settle) agree to share lists of their past lovers. Penn Badgley and Taylor Momsen also star. J. Miller Tobin directed the episode written by Robby Hull & Etan Frankel (#219).