According to FemaleFirst, Miller and Ifans confirmed their relationship after they were spotted kissing in a park in London.
The two actors have always denied being involved with each other despite the numerous photos taken of them together.
A source revealed, "They looked like they were very much in love as they strolled through the park. They were holding hands as they walked the dogs, and then suddenly stopped to share a romantic kiss. Sienna was beaming."