NEW YORK - At the time of Michael Jackson's death last week, it was well-known that he was preparing for a 50-show concert series at London's O2 Arena later this month.

What was less well-known -- and what many are now speculating about -- was what kind of recordings Jackson had done for the last few years.

Billboard has learned that the singer was working on two albums at the time of his death: one in the pop vein that made him famous and another that would consist of an instrumental classical composition. And while some believe the star wanted to recapture his '80s glory days -- or escape financial trouble -- those who worked with him recently say he was motivated by his fans and his children.

Jackson was working on the pop album with songwriter Claude Kelly and R&B star Akon, who says that Jackson was motivated by the ticket sales for his performances.

"He said, 'My fans are still there. They still love me. They're alive,'" Akon says. "His kids are like his first priority, and they had never seen him perform live. He was trying to create the most incredible show for his kids."

Kelly, who wrote "Hold My Hand," the Akon-produced Jackson track that leaked last year, says Jackson never lost his passion. "He was the King of Pop, the biggest to ever do it, and the one thing you never lose -- whether known by the whole world or just 10 people -- is your love for music," Kelly says. "That never goes away, and it never went away for him amidst his troubles."

Composer David Michael Frank had worked with Jackson on a 1989 TV tribute to Sammy Davis Jr. and received a call from the star's assistant two months ago about collaborating again. Jackson invited Frank to his home in Los Angeles' Holmby Hills, told him he was working on an instrumental album of classical music and asked for help with orchestration.

"He had two demos of two pieces he'd written, but they weren't complete," says Frank, who adds that he was impressed with Jackson's knowledge of classical music. "For one of them, he had a whole section of it done in his head. He had not recorded it. He hummed it to me as I sat at the keyboard in his pool house and we figured out the chords. I guess this recording I made is the only copy that exists of this music."

A few weeks ago, Jackson called to see how Frank was progressing on the orchestrations. "He mentioned more instrumental music of his he wanted to record, including one jazz piece," Frank says. "I hope one day his family will decide to record this music as a tribute and show the world the depth of his artistry."

Although questions arose about Jackson's health, and the impact it had on his dancing and singing, those who collaborated with Jackson say his voice was in fine form, despite his frail appearance.

Greg Phillinganes, a keyboardist who collaborated with Jackson as musical director of the "Bad" tour and appeared on several of his albums, says Jackson sounded as good as he ever did. "He still had a good voice and never had a problem singing," says Phillinganes, who last spoke to Jackson in March. "There were questions about him being able to pull off the tour on the choreography side, but sources working with him told me he was dancing all the time, every day, and was very focused, excited and committed to making this tour the best it could be."

Akon last spoke to Jackson three months prior to his death. "He would always tell me to eat right and ask me if I was exercising and drinking water," he says. "He'd always stress you had to take care of yourself before you can go off and do anything else."

Frank agrees. "He seemed totally healthy, not frail, and gave me a firm handshake when we met. He seemed in good health, had a good voice and was in good spirits," he says. "He was very skinny, but from what I knew, he was always thin. He was also taller than I pictured, but he might have been wearing some platform shoes. And he was impeccably dressed."

Much has been made of Jackson's intense rehearsal schedule, but Phillinganes says that Jackson lived up to his reputation as a perfectionist. "It was the biggest comeback of his career, arguably the biggest comeback in pop music -- even bigger than Elvis," he says. "So obviously he'd want to do the best he could. He never did anything half-assed, which is what originally got him to the stature he had."