In a note sent to The Howard Stern Show, Hager said the two former, long-feuding Van Halen bandmates began speaking to each other again earlier this year.
"Eddie and I had been texting, and it's been a love fest since we started communicating earlier this year. We both agreed not to tell anyone, because of all the rumors it would stir up about a reunion, etc., and we both knew that wasn't gonna happen. But he also didn't want anyone to know about his health."
Hager also revealed that Van Halen hadn't replied to him about a month ago, in which he figured things weren't good.
I reached out one more time last week, and when he didn’t respond, I figured it was a matter of time. But it came way too soon.
Soon after the news of Van Halen's death, Hagar posted a photo of the two rockers together, writing that he is "heartbroken and speechless."
Hagar later responded to fans, commenting on the post:
"All the love pouring out from the fans and the news today is all too overwhelming," he said. "You can't imagine the thoughts burning through my brain, my heart, my soul right now. I just want to say, 'It's all good between Eddie and I.' I'll explain another time when this has digested."