Instagram co-founder Mike Krieger received a great Valentine's Day gift from his girlfriend this year. Kaitlyn Trigger, who has been dating Krieger since before he launched his award-winning iOS photo-sharing app, launched an app of her own on Thursday called Lovestagram, a Valentine's Day-themed app that makes interactive Valentine's Day cards using the Instagram API.

Happy Valentine's Day, Mike! Trigger said in her Lovestagram to her boyfriend. Like an Instagram filter, you make my world more beautiful. xoxo, Kaitlyn.

Lovestagram collects all of the Instagram photos that you've shared between you and that special someone -- through username tags, comments exchanged, or photos shot in the same location within an hour of each other -- and creates a slideshow out of them. Just sign into your Instagram account and enter the username of that someone, and Lovestagram lets you see all of your photos, or view them all in one framed collage.

It basically lets you look through your relationship in photos, Trigger said.

The app doesn't require both individuals be in an actual relationship with one another; regardless of status or person, Lovestagram works with anyone and everyone, but be warned: All of the frames around your photos will be love-themed.

What makes Trigger's gesture even more romantic is the length to which she kept this project a secret. Starting last fall, Trigger hatched a plan and began studying code to write and develop the app. Despite having a code expert for a boyfriend, Trigger secretly taught herself HTML, CSS, Django, Python, Photoshop, Jinja and jQuery. She also notes that she had help from her amazing friends -- Krieger included.

Mike was really delighted when he realized I was learning code and I had to fend him off a little, she said. I really did want to build this myself.

Krieger knew his girlfriend was working on a project, but Trigger made sure to keep him off the scent. Krieger supposedly has no clue what Trigger's project is and when it's set to launch, but if he just read this article, he obviously does now.

Trigger says she may later expand the app to work for other holidays in the future, such as weddings or anniversaries.

Since launching Instagram version 2.0 in September 2011, the one-year-old app has amassed more than 10 million users and is seeing a sign-up rate of over one user per second.