Britney Spears' ex-husband Kevin Federline will "always love" his former wife and has promised to always "be there" when she needs him.

Federline, who has full custody of the former couple's two sons, insists Spears will always be important to him as she is the mother of his children, Sean Preston, two, and Jayden James, 18 months.

The dancer/rapper also lavishes praise on his ex-girlfriend, Shar Jackson, who is mother to his two other children - Kori Madison, six, and Kaleb Michael Jackson, four.

He says, "I will always love the mothers of my children, and I will always be there for both of them. I believe that any good energy I put out there brings more good energy into my own life. The relationships with my kids and family will last my whole life and are the most important to me."

And Federline is determined that his children with Spears will grow up in a happy, stable environment.

He says, "Their needs define my schedule every day. It is so very important to me that my children will always know and never question, that no matter what happens, they have a mummy and daddy who love them very much."

Federline was granted full physical custody of the boys last year after Spears failed to adhere to court-ordered medical tests.