ABCs Greys Anatomy is poised to become the longest-running primetime medical drama in U.S. television history this week, surpassing ER , which previously held that title , The Hollywood Reporter reported.

The medical drama, currently starring Ellen Pompeo, Jesse Williams and Justin Chambers, will air its record-breaking 332nd episode on Thursday. Shonda Rhimes, the shows creator and executive producer, celebrated the milestone on Twitter Wednesday.

A lot has happened in 332 episodes and tomorrow we become the longest-running primetime medical drama, she wrote. People. You dont want to miss this!

Greys, which is currently in its 15th season, debuted in March 2005 with an episode titled A Hard Days Night. Thursdays episode, We Didnt Start the Fire, will surpass the 331 episodes of NBCs ER, which ended its 15th and final season in 2009.

Pompeo, the actress-producer who plays Meredith Grey on the ABC drama, commemorated the shows record-breaking episode in a post on Instagram touching on the incredible journey.

We started this journey 15 years ago and this weeks episode makes history, she wrote on Wednesday. The truest thing about this journey is we appreciate how incredible it is.