A picture shows the two in an embrace with a large diamond ring on her left ring finger.
"It'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".
In a post in December, Pratt marked Schwarzenegger's 29th birthday by sharing a picture collage of them together.
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The assailant raised his arms triumphantly to the crowd after the attack, before being tackled and arrested by security guards. One eyewitness told broadcaster TVN that the man appeared "happy with what he had done".
Chris Pratt, 39, and Katherine Schwarzenegger, 29, reportedly started dating a year ago in June. I've cherished our time together. The couple were married in 2009 and had son, Jack, in 2012. Thrilled God put you in my life.
Katherine is the elder daughter of actor and politician Arnold Schwarzenegger and broadcast journalist Maria Shriver.
Pratt and ex Anna Farris announced that they were splitting in summer of 2017 following eight years of marriage.
Cape Town - Has Chris Pratt moved on?