The 30-year-old actress was first romantically linked to the musician in 2017.
Congrats to Elizabeth Olsen!
The 30-year-old actress is engaged to her boyfriend, Milo Greene frontman Robbie Arnett, according to multiple reports. ET has reached out to Olsen's rep for comment.
Olsen and Arnett have been romantically linked since March 2017, and made their first red carpet appearance as a couple in September that year.
The Avengers star has stayed private about her personal life, telling Modern Luxury magazine in 2017 that she's learned tips on how to handle reporters from her older sisters, Mary-Kate and Ashley Olsen.
"They're very tight-lipped -- notoriously so. I was not caring what I was saying [in interviews] because I'd assumed no one would read it," she explained.
"They'd say, 'You know, even if you don’t think anyone’s going to read this article, someone might pull the quote later for [something else].' It's all part of how you hope someone interprets you, and how they frame who you are and the work you do," Olsen added.
The actress' engagement news comes just after rumors sparked that Ashley was engaged to her boyfriend, Louis Eisner, after being spotted with a ring on that finger. Mary-Kate has been married to Oliver Sarkozy since 2015.
See more on the family in the video below.