Sort of.
Look basically, Tegan & Sara sing some words on a new song by LA-based duo Night Terrors of 1927 called 'When You Were Mine'.
The song's taken from the latter's second EP 'Anything To Anyone', which is out in America this week at some point, and you can listen to 'When You Were Mine' below right now:
Tegan and indeed Sara need to hurry up with this new album of theirs, don't they.