The "Uptown Funk!" hitmaker was first spotted on a dinner date with "Mr. Robot" star Grace in New York last September (2020), and on Saturday, May 22, the happy couple was photographed hugging and kissing while out for a walk in London.
However, it wasn't just the public display of affection which has drawn attention - the images show Grace rocking a lone sparkler on her left hand.
According to the New York Post's Page Six, the loved-up pair spent part of Saturday having lunch with Mark's mother, Ann Dexter-Jones.
In early March, it was reported that Mark is "definitely dating" Grace. A source told The Sun newspaper at the time, "Things have become romantic."
"Lockdown restrictions have made things more difficult, especially when he has been back in the U.K., but they are seeing how it goes and are getting along," the source added. "Mark is pretty private, so he has kept the whole relationship low-key but it really seems to be heating up."
Representatives for the stars have yet to comment on the news, which emerges nine months after Grace, the daughter of Meryl Streep and Don Gummer, finalized her divorce from Tay Strathairn.
Meanwhile, Ronson's 2011 marriage to French actress and singer Josephine de La Baume officially ended in 2018. Since then, he was reported to have romanced British actress Genevieve Gaunt and "Saturday Night Live" talent executive Rebecca Schwartz.