The 32-year-old star uploaded romantic pictures of her and the Argentinean model on micro-blogging website twitter and wrote that she had fallen for her new man.
She tweeted: "Es todo un tierno. Lo amo," which roughly translates as "It`s all tender. I love him."
The beauty`s emotional revelation has emerged just days after she filed for divorce from cage fighter Alex Reid after 11 months of marriage.
However, she has defended her decision to quickly move onto another relationship, claiming her estranged husband has also been involved with someone else.
Soon after saying she loved Leandro she tweeted: "people forgetting alex sh**ged a girl in manchester few weeks ago and she did kiss and tell on him!...I will do what makes me happy. (sic)"
Katie - who has three children from previous relationships, Harvey, eight, Junior, five, and three-year-old Princess Tiaamii - was spotted kissing Leandro at Elton John`s post Oscars party on February 27 and has been seeing him since.
The hunk flew to Britain to visit the model soon after and said that although he was enjoying spending time with Katie he didn`t want to become famous because of her.
He explained: "We are just getting to know each other, and you never know...I would like to keep getting to know her.
"In my country I didn`t become famous for the people I`ve been seeing, but what I`ve done. I have always protected the people I have been with."