Billy Corgan found Lisa Marie Presley's death "really hard".
The Smashing Pumpkins frontman performed at the funeral of the singer following her shock death at the age of 54 in January and he has paid tribute to his friend as a "really, really cool" person.
Appearing on SiriusXM's 'The Howard Stern Show', he said: “She was awesome — that was a tough one.
"That was really hard for me because she was a one-of-a-kind person and the world really didn’t know her because they, of course, always knew her as Elvis’ daughter, but she was a really, really cool, unique person.”
Billy previously co-wrote 'Savior', a hidden track off Lisa Marie's 2003 debut album 'To Whom It May Concern', and he admitted he regrets not working with her more on the record but he was too busy.
He said: “I wish I’d sort of taken more possession of it because she never really got her music thing off the ground.
“She was actually really talented … If you get a chance to hear her voice, she inherited a lot of her father’s great depth and the voice and it’s a shame that she didn’t make more music.”
The 'Tonight Tonight' hitmaker thinks he got to know Lisa Marie's legendary late father, Elvis Presley, through his friendship with the star.
He said: “She did remember him, and she had really glowing things to say about her father.
“I got to know her father through her in a way that I’ve never seen him in public. So, I got this like front-row seat of what Elvis the person was like and, if you know what Elvis the person was like from her perspective, Elvis is even more amazing.”
But Billy believes some of Elvis' career choices, including making "shlocky movies", have put a dampener on the 'Suspicious Minds' singer's legacy.
He said: “If you look at it completely from a musicology point of view, he’s arguably the single most important music artist since they started recording artists because no one changed things more than he did.
“His talent was at a level that’s almost incomparable … but unfortunately, it’s mixed with a lot of things where people don’t see the talent because he just comes across as a personality.”