The two were photographed on a boat in picturesque Mykonos, Greece.
Greene's 'Twilight' co-star Robert Pattinson was reportedly in attendance, alongside celebs like Zac Efron, Liam Hemsworth and Brittany Snow.
The pair have been inseparable.
A source told ET last week that the two have been 'casually dating' for about a month.
The news comes just days after the rapper gushed about Halsey during an interview with ET.
The proud new husband also shared the hilarious promises he made in his wedding vows.
ET takes a look at 'The Bachelor' couples who are still going strong.
Cuoco told ET before her nuptials that 'there will be no animals left behind' when she said 'I do.'
The singer was spotted with a new tattoo on her foot earlier this week.
The twosome had called it quits earlier this year.
Jonas recently made his relationship with the actress Instagram official.
A source tells ET that the couple couldn't have looked happier during their night out in Los Angeles on Monday.
The musician paid tribute to 12 years of marriage and 'celestial' dancing with his gorgeous wife.
The reality star also opened up about the 'enormous rebuilding' going on at home.
