Dune (German happy hardcore/progressive trance band)
Some post-Verena Dune releases were credited to "Dune & The London Session Orchestra," "Dune Featuring Vanessa," and (in the case of their dance versions of "Star Trek: Voyager: Main Title") to nobody at all.
Also see solo releases/side projects under DJ Raw (Oliver Froning), Verena (Verena von Strenge and Bernd Burhoff), and Anna (Jens Oettrich, Bernd Burhoff, and backup dancer Anna), and 1000 People Parade.
All of the releases with the London Session Orchestra were covers, arranged by Oliver from Dune, sung by Dune's singer-of-the-week (Vanessa the first time, Tina the second), but using a real orchestra instead of Oliver's usual sequencer and synths.
The collaboration was supposed to be a one-off for a single, but it was so successful, and they had such a good time, that they recorded an entire album, which spawned another single. Then they went their separate ways.
After Dune's replacement singer left and the new album was shelved, Oliver found a new singer, went back to the orchestra, and released another album, which also spawned a single. They went their separate ways again, and it seems to have stuck.