Created by Paul Dini and Bruce Timm as the Joker's sidekick for Batman: The Animated Series, a 1992-1995 Tim Burton tie-in cartoon that ended up transcending its source material to contribute characters to the official DC comics universe, Harley Quinn is perhaps the show's most popular and long-lasting creation. Joining comic canon in 1999, Harley Quinn is the Joker's fervently loyal girlfriend, though their relationship has proven rocky in the past. Naive and abused, she'll usually do anything for her "Mr. J," but will occasionally separate from him as a result of the way he treats her.
During these breaks, she'll often stay with fellow Batman supervillainess Poison Ivy, to the point where Poison Ivy has specially inoculated Harley to be immune to her poison so they can "play." A much more nurturing relationship than she has with the Joker, Harley Quinn's time with Poison Ivy shows the true potential she could have as a criminal mastermind if the Joker would loosen his reins on her. A popular duo, fans have oft-speculated if there's something more going on between Harley Quinn and Poison Ivy than just a close friendship, and during a special Twitter event last Friday where Harley Quinn writers Jimmy Palmiotti and Amanda Conner were taking questions over the official DC Twitter account, one fan took the liberty of asking, "Are Harley and Ivy girlfriends? Please confirm this." Later, the official response came in loud and clear: "Yes, they are girlfriends without the jealousy of monogamy," confirming a relationship between Harley and Ivy, and hinting that it may even go on while Harley is with the Joker.
While we might have preferred an explicit in-comics confirmation, we couldn't be happier for Poison Ivy and the clown princess of crime.