When Apple unveiled iOS 5 last fall with Twitter integration, the big question on everyone’s mind was “Where’s Facebook?” Apple had reportedly been in talks to bring Facebook integration to iOS since before iOS 4, but nothing had ever come of it. When iOS 5 came out with Twitter integration but no Facebook (a feature that appears to carry over to OS X 10.8 Mountain Lion, coming later this year), it raised a lot of eyebrows.

Last night at AllThingsD’s D10 Conference Apple CEO Tim Cook spent some time on stage with Walt Mossberg and Kara Swisher, talking about Apple. During that talk, Cook strongly hinted that iOS would be getting Facebook integration in the not-too-distant future. When asked about the situation by Mossberg, Cook said that he thought the relationship between Facebook and Apple was “very solid,” pointing out that “I saw Sheryl earlier, you can ask her” (referring to Facebook COO Sheryl Sandberg). He went on to say that he had “great respect for them,” and that iOS users should “stay tuned on this one.”

Of course, there have been difficulties between the two companies in coming to an agreement in the past, Swisher noted, pointing out that Steve Jobs said that Facebook was “onerous.” She asked Cook if he thought Facebook was onerous too. Cook paused briefly before saying “they have their way of doing things,” a remark that drew laughter from the crowd.

Swisher pressed him further, asking whether Apple and Facebook were “must-haves for each other.” Cook replied that Apple’s goal is to “provide customers simple and elegant ways to do the things they want to do,” and that as such he wanted customers to have the best possible experience when using Facebook on their iPhones or iPads, “so stay tuned,” he repeated.

These remarks echo comments made by Cook earlier this year. Back in February Cook addressed a meeting of Apple’s shareholders. When asked by one whether Facebook is “friend or foe,” Cook said that Facebook is a friend and noted the enormous overlap between Facebook users and Apple customers. He also pointed out how good for Twitter iOS integration has been, and suggested that Apple and Facebook “could do more together.”

So there you have it. While Cook did not outright promise that Facebook integration would be coming in iOS 6 (or OS X Mountain Lion), it’s pretty hard to avoid the impression that it will at least be coming fairly soon.

Check out the video of Cook’s discussion of Facebook below: