Mariah Carey wishes she had done a better job performing Jackson 5's biggest hit, "I'll Be There," at Michael Jackson's memorial Tuesday at Los Angeles' Staples Center.

In a post on her Twitter page, the singer (who wore a black Jenny Packham gown to the service) says she was just too overcome with emotion. As Carey sang the song with frequent collaborator Trey Lorenz, photos of Jackson flashed on a huge screen above them.

"Trying to sing today was basically impossible for me," writes Carey. "I could barely keep myself from crying. I'm sorry that I wasn't able to pull it together and really do it right, but I was literally choked up when I saw him there in front of me."

"One thing I know is, we will never really have to say goodbye to MJ. His legacy lives on through his music and the millions of people. He inspired with his timeless music. He will be forever in our hearts," she adds.