Mark Aug. 31 on your calendars, but make sure it’s not in Sunrise. The popular calendar app, which was acquired by Microsoft last year and promptly merged into Outlook (which was formally Acompli, another Microsoft acquisition), has announced it will officially shut down.

We knew this day was coming, but it’s still hard news to swallow. Sunrise has remained one of the strongest calendar apps in mobile, providing users with a clean UI and great features. The calendar will continue to live on in Outlook, but it will never be the same.

Here’s what the Sunrise team had to say in a blog post on Wednesday:

As all good stories go, there’s a sad bit to it: we’re not able to suppose and update Sunrise anymore. No new features. No bug fixes. For us, that’s the definition of a lousy app and it’s not a user experience we want to leave you with. For this reason, we’ll be removing Sunrise from the app stores in the next few days.

The Sunrise team says they’ll continue to work closely with the Outlook team, with the goal of “making your day-to-day life easier and more enjoyable to manage.” That’s a great sentiment, but it’s still a sad day for longtime Sunrise users (me).

I’ve used Outlook’s calendar but it’s not the same as having a standalone app. Sadly, the Sunrise we all knew and loved will soon be gone for good come Aug. 31.