In London to unveil her new album at a VIP party Tuesday night, Whitney Houston – looking glam in a black and white Dolce & Gabbana gown – signaled she was back.
With her mentor, music mogul Clive Davis, playing nine tracks from her upcoming album to be released in September
, Houston, 45, "looked radiant," a source at the party at the Mandarin Oriental Hotel tells PEOPLE.
"She gave an amazing speech saying how much the album comes from the heart and telling of her love for Clive Davis," the source added. "She was also saying how much she loved being in London … and you could tell she was happy to be here."
The CD will be Houston's seventh studio album and represents a comeback after a seven-year hiatus that included some well-publicized troubles. As for the album, some of the songs were finished and others not, a source tells PEOPLE.
Thanking Davis, Houston told party guests, "When Clive called me I was pretty ready to buy my island home [and retire], but he said, 'No, you're going to sing again, people want to hear you,' " reports Billboard.com
She added, "I hope that these songs stay with you for a lifetime." Davis assured the crowd that "you won't forget it after you hear it."
Among the tracks heard were the title song "I Look To You," by R. Kelly, and an Alicia Keys song, "One Million Dollar Bill." Also included was a Diane Warren-penned song, "I Don't Know My Own Strength," and a duet with Akon, "Like I Never Left."