Whitney Houston reportedly had a year-long affair with Jermaine Jackson.
The late-singer died at the age of 48 last month. It is alleged that she became close to Michael Jackson's brother when he was brought in to work with her early in her career in the mid 1980s, and although he has previously claimed they had strong feelings for each other in an autobiography, it is now believed they were "lovers".
A source told the Sun on Sunday newspaper: "Jermaine didn't tell even half the story in the book.
"He made it sound like they flirted and backed away. But they were lovers. In those early days with Whitney, he was smuggled into her hotel rooms, they worked extra late in the studio and she even had a codename for him. She referred to him as 'Jai'."
However, the romance fizzled out when he refused to leave his then-wife Hazel Gordy.
The friend added: "The reason it ended was because Jermaine wouldn't leave his wife, and Whitney was angry. The video for 'Saving All My Love For You' was about all of that."
Jackson - who split from Hazel in 1988 - is believed to have been particularly upset by Houston's recent death because it echoed that of his brother Michael, and although he did not attend her funeral in New Jersey he remains close with her family.
The source added: "Jermaine remains on good terms with Whitney's family. He knows they know. But Whitney was no husband-stealer. She just happened to fall for a married guy."