Chris Pratt & Katherine Schwarzenegger Make It Instagram Official

On Thursday, Pratt posted a tribute to Katherine on Instagram. Along with a collage of pics, he wrote, “Happy Birthday Chief! Your smile lights up the room. I've cherished our time together. Thrilled God put you in my life. Thankful for the laughs, kisses, talks, hikes, love and care.♥️🍾🎉🎂.”

In response to the sweet post, Katherine said, “I love you,” with three heart emojis.

The pair seem to have gotten serious over the past few months! A source recently told People magazine, “They're such a great fit together. t's only been a few months but Chris and Katherine are both very serious about the relationship and their friends wouldn't be surprised if they got engaged sooner rather than later.”

The insider added, “Katherine has spent time with Chris' family and they all love her too. She fits in really well with them and vice versa.” Schwarzenegger is the daughter of Arnold Schwarzenegger and Maria Shriver, and the grandniece of President John F. Kennedy.

A few days ago, Pratt got in some bonding time with Katherine's brother Patrick at the Clippers game.

Chris spent Thanksgiving with Katherine's family. Another source told the publication, “You can tell Chris knows Katherine's family really well. Chris always seems very comfortable around her family. It's like he is part of the family.”