It looks like OnePlus is up to something, as the company has just teased an event or announcement of some sort for April 20.
OnePlus took to Google Plus today to post an image saying "You're Invited" to something on April 20, but we aren't quite sure what that something might be. Along with the image, the company says "From here on out, anything could happen." It's possible that we could get a look at this year's follow up to the OnePlus One, the OnePlus Two. However, it was revealed earlier this week that that device is pegged for a third quarter release date.
In any case, we'll know much more when whatever OnePlus has in store is revealed on April 20.
Source: OnePlus (Google+)