The 'Harry Potter' star has been in a relationship with the actress for "about two years" after meeting her on the set of 'Kill Your Darlings' in 2012, according to the MailOnline.
The couple went public with their romance over the weekend as they were spotted doing the grocery shopping together in New York City, but they have done well at keeping their relationship a secret over the past 24 months as it was previously believed they had called time on their brief fling shortly after it began in 2012.
The 24-year-old hunk split from his previous girlfriend Rosie Coker in October 2012 after two years of dating and reportedly tried to woo Erin not long afterwards.
However, it was believed Erin was left "devastated" when he apparently ended their brief relationship.
A source told Life & Style magazine at the time: "Erin thought it was a real relationship, going as far as introducing Daniel as her boyfriend. He's flown her out to London and taken her on dates and spent plenty of time with her in NYC, but Daniel just up and left New York without a second thought. Erin was devastated."
However, the split didn't last long as the pair were spotted with each other again in London last August.