The message to fans included a clip of Lopez admiring a huge, green diamond on her ring finger, an image of which was also shared by her sister on social media.
Lopez teased the "major announcement" with a video on Twitter that same night. "So I have a really exciting and special story to share..." Lopez told her followers.
She also added a diamond ring emoji to her Twitter handle.
saying, "We're older now, we're smarter, we have more experience, we're at different places in our lives, we have kids now, and we have to be very conscious of those things."
Lopez and Affleck previously began dating in July 2002 and got engaged that November before postponing their September 2003 wedding just days before the date.