Yup, if you've forgotten, it was Luna Lovegood who told Harry about the lost diadem of Ravenclaw.
Luna Lovegood Costume Spectre Specs | Harry Potter Accessories If we've convinced you that seeing the world through Luna's eyes would be pretty delightful, amusing, and very thought-provoking, then you'll love wearing these SpectreSpecs!Fans of the nonconformist blonde Ravenclaw witch will love sporting these officially licensed glasses, featuring a uniquely shaped frame and wacky purple lenses. Are you sick of Wrackspurts floating through your ears, making your brain go all fuzzy? If so, you definitely need a pair of these Luna Spectre Specs!It's safe to say that Luna is eccentric but her eccentricity is what makes her so helpful to Harry and the rest of Dumbledore's Army. First of all, she's able to sense Wrackspurts, she's a whiz when it comes to spotting Nargles, and she also helped lead Harry to find one of the last Horcruxes.