updated 02/11/2012 AT 9:00 PM ET
•originally published 02/11/2012 AT 10:00 PM ET
Carey, who collaborated with Houston, 48, on “When You Believe” – a song from the Prince of Egypt soundtrack – is “heartbroken and in tears” over Houston’s passing, she wrote on Twitter Saturday.
Calling the former Bodyguard star “incomparable,” Carey Tweeted her “heartfelt condolences to Whitney’s family and all her millions of fans around the world.”
Adds the singer, “She will never be forgotten as one of the greatest voices to ever grace the earth.”
Other people close to Houston have also expressed their upset on the social networking site.