Joaquin Phoenix and Rooney Mara are engaged.

The 'Joker' actor and the 'Girl With The Dragon Tattoo' actress are set to tie the knot, three years after they started dating, US Weekly reports.

Joaquin and Rooney were rumoured to be engaged back in May when the actress was spotted with a huge diamond sparkler.

Rooney and Joaquin reportedly underwent a secret ''blessing ceremony'' back in June 2017 to prove their commitment to one another.

A source said: ''They are faced with a long separation as he'll be shooting in either Australia or New Zealand. It's a looming threat. It's why they decided to have the ceremony. It was Joaquin's idea, just to show how committed he is to Rooney and to ease her nerves about him being away for so long. His pals and a small group of hers gathered in the garden at his house. It was all very simple. They exchanged promises to be a true couple and everyone threw flowers on them. Even though it's nothing legal, it was really sweet. You can tell she's really won his heart and no one is more surprised about it than him.''

While Rooney and Joaquin have gone to great lengths not to be photographed together until their recent appearance at the Cannes Film Festival, friends realised just how serious their relationship is when the actress moved to Los Angeles.

The insider told Grazia magazine: ''Rooney is smitten and she has broken her vow to never live in LA in order to be closer to Joaquin. All of her friends knew it was serious as soon as that happened because she's always hated LA.''