The 30-year-old actress fell head over heels for the filmmaker on the set of 2011 movie 'Big Sur' and admits her fiancé is the ''ideal'' partner whom she always fantasised about meeting as a child.
She said: ''I had forgotten my ideal relationship. When I go home to my childhood bedroom I see all the quotes I wrote about meeting a soulmate.
''Just through growing up and having relationships that didn't work I forgot that side of things and it became about, 'How do we make this work?' When I met Michael all of that magical side of believing in a soulmate returned.
''I'm really grateful because I believe it's rare. I believe that we're two people who have found their way though difficulties in life, unpacked their baggage and realise it's the same baggage.''
The 'Blue Crush' star is excited about their upcoming wedding and becoming an official stepmother to Michael's 15-year-old daughter, Jasper.
Kate gushed: ''She's 15 and she's wonderful. A lot of people say it must be really difficult, but it's been such an effortless, beautiful, gorgeous relationship for me. We have a blast together, the three of us. I love it.''
The blonde beauty refused to give anything away about their upcoming nuptials, but hinted the ceremony would celebrate their American heritage.
She said: ''[It] will be a love letter to our country. It's funny because I didn't really think about marriage very much. I was not the girl carrying around bridal-dress designs.''
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