Fans who watchGreys Anatomyknow that the long-running medical drama is famous for its epic crossover events. First, the crossovers happened with characters from its first spinoff,Private Practice, but now they occur withStation 19. However, what viewers probably dont know is that these events only began because of this one real-life crisis during the filming ofGreys AnatomyandPrivate Practice in 2007.

In the early 2000s,Greys Anatomybecame a pop culture phenomenon. To capitalize on its success, ABC pursued a spinoff featuring Addison Montgomery (Kate Walsh). To test out the new series, ABC aired a two-hour special,Greys Anatomy, which aired on May 3, 2007.

The backdoor pilot featured Addison leaving Seattle Grace Hospital to visit friends in Los Angeles, California. While visiting Naomi (Audra McDonald) and Sam Bennett, she ends up performing surgery. Naomi is a fertility specialist, while Sam practices internal medicine. They both own and work at the Oceanside Wellness Group. Their private practice focuses on a whole-body approach to medicine.

Addison fell in love with the small practice and the beachside life that her friends lived in LA. Instead of returning toGreys Anatomy, Addison decided she needed a change in her life. She became the new OB/GYN at Oceanside Wellness and the star of the spinoff medical series,Private Practice. The backdoor pilot episodes were part ofGreys AnatomySeason 3. They garnished so many viewers that the spinoff became part of the fall lineup on ABC in 2003.

Private Practicebegan season 1 in the fall of 2007 with nine episodes airing. However, theWriters Guild Strike of 2007/2008caused a delay in the remaining episodes for the season. The spinoff series ended with 13 episodes ordered but never produced.

The strike lasted from Nov. 5, 2007, to Feb. 12, 2008. All 12,000 film and television screenwriters of the American labor unions went on strike to demand an increase in funding for the writers.

RELATED: Greys Anatomy: Ellen Pompeo Hints at the Shows Ending Im Not Trying to Stay on the Show Forever

After the strike, ABC decided that Addison should return toGreys Anatomysince there were no furtherPrivate Practice episodesfor her to return to. She returned for only one episode, but it was so successful that the idea of a large-scale crossover event was born.

Both creative forces behindGreys AnatomyandPrivate Practicefelt that a crossover was something they wanted to do. The event was much larger than only Addison returning to the show. The crossover included stars from both shows.

Addisons brother was rushed to Seattle Grace hospital because of parasites in his brain. Derek Shepherd (Patrick Dempsey) performed the successful procedure that saved his life. Meanwhile, Addison treats one of Dereks patients. Both Sam and Naomi were also included in the crossover storylines.

Following the crossover events success,Greys AnatomyandPrivate Practiceproduced five more similar events. WhenStation 19becameGreys Anatomysnext spinoff, they did the same thing with the new series.

The rest is here:
'Grey's Anatomy' and 'Private Practice' Crossovers Stemmed From This 1 Crisis Off-Screen - Showbiz Cheat Sheet