Chris Pratt's birthday collage for Katherine (c) Instagram

Chris Pratt is engaged to Katherine Schwarzenegger.

The 'Guardians of the Galaxy' actor has proposed to his partner - the daughter of Arnold Schwarzenegger and Maria Shriver - after a whirlwind romance over the summer.

Sharing a romantic snap of the pair on Instagram with Katherine's engagement ring on show, Chris wrote: "Sweet Katherine, so happy you said yes!

"I'm thrilled to be marrying you. Proud to live boldly in faith with you. Here we go!"

It is the first relationship the 39-year-old star has been in since his split from ex-wife Anna Faris in the summer of 2017, while the former flames finalised their divorce in November.

Although Chris and Katherine have only been together since June, it was previously said that they are both "hopeful for the future".

A source recently said: "They're both serious about the relationship and hopeful for the future.Chris doesn't just date to date, and neither does Katherine.

"She's very excited... [They] are very happy together. They're very compatible and have a lot in common."

Meanwhile, the couple's happy news comes after Anna - who is dating Michael Barrett - said she and Chris "work really hard" to be supportive of each other in the wake of their split for the sake of their six-year-old son Jack.

She previously revealed: "Chris and I work really hard 'cause we have Jack, that is sort of the long game idea and making sure Jack is really happy, which makes us really happy. We have sort of the luxury of circumstance.

"You know, we are both in other loving relationships ... but it is ... it's like how do you not in general sink into a place of bitterness?

"I do want to reiterate though, that I f***ing acknowledge, we all do, everyone acknowledges, that there is bitterness and pain with all breakups and that hopefully makes us all human. But the long game is just the worst being the bigger person. It just is. It f***ing sucks until, then what happens though, is that everyone's happy."