According to People, she had been spotted by paparazzi in NY wearing an engagement ring.This will be Mellencamp's third marriage and Ryan's second.
ExtraTV reports the couple has been dating on and off since 2011.
According Fox News the couple's relationship has been tested with challenges over the years, including long-distance issues, breakups and attempts to move on with new partners. He and his third wife, model Elaine Irwin, split in 2010 after 18 years of marriage.
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After saying that the actress "hates him to death", he added: "Oh, women hate me". "She just doesn't want anything to do with me, and I don't blame her". I loved Meg Ryan.
Ryan's union to Mellencamp will mark her second marriage and his fourth.
'I throw fits, I gripe, I complain.
Meg is 56, was married to Dennis Quaid from 1991 - 2001 and has 2 children, Jack Quaid and Daisy True Ryan, her adopted daughter from China. I'm moody. Every bad thing that a fella can be, that's me, ' he told Stern.
Mellencamp has previously been married three times.