After the announcement of the Nokia 808 Pure View running on Belle FP1, many believed Carla, the much anticipated update to Belle, would be renamed Belle FP1, but that seems not to be the case at all.
Ali over at My Nokia Blog found a bug report detailing mentioning bugs found in Carla that were not present in Belle FP1 and FP2, meaning Carla would likely not be either of those. This would be pretty good news to those still loyal to what used to be Symbian, as rumours previously suggested that Carla and Donna would be the only updates after Belle was released. No word yet on when the Carla update would become available, but Belle FP1 is rumoured to come out in June, just after the Nokia 808 becomes available.
Source : My Nokia Blog