Chris Pratt and Katherine Schwarzenegger are Instagram official

Chris Pratt and Katherine Schwarzenegger went public with their romance on Thursday.

The "Guardians of the Galaxy" star posted a sweet birthday message to his girlfriend, who he affectionately called "Chief."

"Happy Birthday Chief! Your smile lights up the room," Pratt, 39, gushed on Instagram. "I've cherished our time together. Thrilled God put you in my life. Thankful for the laughs, kisses, talks, hikes, love and care."

The sweet collage was the first time Pratt posted photos with Schwarzenegger, 29, with whom he's been linked since June.

Last month, Pratt and Schwarzenegger — daughter of legendary action hero Arnold and ex-wife Maria Shriver — teamed up to help fundraise for a friend who lost his home in the devastating Woolsey fire in California.

The "Avengers: Infinity War" actor is said to be smitten with Schwarzenegger, who's already bonded with his son, Jack, who he shares with ex-wife Anna Faris.

Pratt and Faris, 42, separated in August 2017 and finalized their divorce in October 2018.