he fourth season of the American television series 90210 was announced by The CW on April 26, 2011. It was later announced it would return to its original Tuesday 8:00 pm time slot, as a lead-in to new series, Ringer, and premiered on September 13, 2011.
Trevor Donovan was dropped as a regular, as a result of ongoing changes by the new showrunners. He returned as a guest star in the fall to conclude his storyline. However, in late February 2012, it was reported that Donovan will return near the end of the season. The CW ordered two additional episodes for the season, which will total at 24. It has also been announced that the show will get a fifth season.
Season four opened to a 0.9 rating in adults 18–49, even with last season premiere. The series returned from its mid-season break on January 17, 2012, one week later than originally announced.Overview from themoviedb.org