Leighton was 21 when she made her debut as Blair — though the star originally auditioned to play Serena, and needed to dye her blonde hair brown for the role of Constance's Queen Bee.
She appeared in a few movies while the show aired, including The Roommate, Date Night, That's My Boy, and Country Strong, and also released music.
Daily Mail Online's FEMAIL here, your one and only source into the not-so-scandalous lives of the Gossip Girl elite.
The hit CW show based on Cecily von Ziegesar's novels is turning ten this fall, with September 19 marking a decade since the seven-season show premiered.
The 30-year-old has gone on to star in two more TV shows post-GG: Wicked City, which ran for eight episodes, and now the new White Gold — in a role many find familiar to Chuck Bass. Though he dated co-star Jessica Szhor during a few seasons of Gossip Girl, the pair split in 2010.