Retna Ltd. 1 / 2

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

Photos: Mariah Carey

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."

Photos: Michael's memorial

"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 [h]e inspired with his timeless music. He will be forever in our hearts," she adds.

More on Wonderwall:

Photos: Michael Jackson through the years

10 ways we want to remember Michael Jackson

Brooke Shields: "Michael Jackson was 'asexual' to me"

More on MSN:

Mariah Carey then and now

More on US Weekly:

See photos from Michael Jackson's memorial


Look back at photos of Michael Jackson and his children through the years