E! News has reached out to Kate and Justin's reps for comment and has not heard back.
The news of their impending nuptials comes more than a week after the actress stirred engagement speculation when she was spotted wearing a certain accessory—a sparkling diamond ring—while arriving with the Dodgeball actor to Vanity Fair's Oscars 2023 after-party.
It also comes after Kate reportedly finalized her divorce from director Michael Polish. The pair, who wed in 2013, had announced their separation in Sept. 2021.
Kate, 40, and Justin, 44, first sparked romance rumors in late 2021, months after an affectionate Instagram exchange over their recent projects together. (The films House of Darkness and Barbarian were released in 2022.)
"There are some movie experiences when you learn a lotttttt about another person. Well, we just wrapped one of those," Kate wrote in May 2021. "Holy moly @justinlong you are a truly spectacular / fun / funny / kind / rare / thoughtful / totally. fckn. rad human being."
Justin wrote in response, "I'm going to say even nicer things about you publicly because people should know what a rare gem you are - all the things you said about me but a little bit (or a lot) more. It was a true joy to be in your glow."
A joint trip to Hawaii followed in April 2022 and the next month, the stars confirmed their relationship on Instagram with a photo of themselves sharing a pint of Guinness while on vacation in Ireland. The actress commented on the post, "I'm the luckiest."