HTC's U Ultra and HTC U Play have already hit the store shelves, meaning, the Taiwanese handset maker's work for at least the first half of the year is done. Well, not really.

If a recent teaser on HTC Taiwan's Facebook page is anything to go by, the popular tech firm might still have a few aces up its sleeve. The update advises tech buffs to get ready for an "unexpected surprise," and the date mentioned in the cryptic message is Monday, March 20.

Although HTC has kept details about the update under wraps, an accompanying image with text that reads, "Spring is coming," seem to have added more fuel to the already burning rumors about the puzzling Facebook teaser. Although tech gurus are hazarding all sorts of guesses regarding what exactly this could allude to, HTC continues to remain tight-lipped about the message and might only divulge shreds of information on the date mentioned in the update.

Lining with this, DroidLife believes the Facebook update might actually allude to the company's shot at reviving HTC 11. Apparently, the company might be planning to breathe new life into the seemingly dead brand. Or, does that mean the previously teased Snapdragon 835 powered HTC phone is just around the corner?

But, with the recent launch of the U Ultra and U-Play smartphones, that seems highly unlikely, unless, the device is a Taiwan-only smartphone. Nothing is set in stone and HTC is clearly in no mood to divulge more details.

Another theory running rampant online hints at HTC's unannounced mobile VR product; though the floral design used in the image is a far cry from any sort of VR revelations. Meanwhile, a recently surfaced report from PhoneArena suggests the green color scheme could either be referring to the sapphire screen, 128GB HTC U Ultra edition, or a new green color variant for an existing HTC phone.

Do you think HTC might drop more clues about the vague Facebook update in near future? Share your thoughts in the comments section below!