She posted a doodle of herself with Mellencamp and captioned the post "ENGAGED!"
While it's unclear is Ryan pursued other relationships in that time, Mellencamp reportedly dated model Christie Brinkley for over a year.
After saying that the actress "hates him to death", he added: "Oh, women hate me".
Mellencamp also took responsibility for the animosity: "I think it's because I'm a child".
Talk of an engagement began after Ryan was spotted wearing a new sparkler on her ring finger on Wednesday in NYC (inset above).
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Instead they must now wait for the remaining games against Valencia and Young Boys to seal their passage to the next round.
'I throw fits, I gripe, I complain.
The three-time Golden Globe-nominated star of "Sleepless In Seattle" and "You've Got Mail" confirmed the news by posting a quirky sketch of the couple on Instagram Thursday. "I'm moody. Every bad thing that a fella can be, that's me".
Mellencamp's comments on the Howard Stern Show were rare as neither he nor private Ryan have shared much publicly about their romance.
The thespian was previously married to Dennis Quaid, while the musician was previously married to Priscilla Esterline, Victoria Granucci, and Elaine Irwin.
In 2006, Meg adopted her daughter Daisy, now age 14, from China.