A source told Britain's The Sun newspaper: "This relationship is the real
thing. She has been following him around like a lovesick puppy.
"She flew to Texas to join him at the SXSW festival then the band returned
to Britain. But they hated being apart and on Friday she flew to London and
is staying in his flat.
"No one is sure how long she will be here for. She is filming in Europe soon
so she could be in London a fair bit."
Kirsten met Johnny earlier this month after she watched his band performing
in Los Angeles.
They were later seen kissing at the SXSW festival in Texas and dirty dancing
at the Blender House party.
Johnny, 26, reportedly finished his relationship with his long-term British
girlfriend to be with Kirsten.