Alfonso Valiente - who split from Nicole's mother Rosemary when she was six but remains close to his daughter - told the Mail on Sunday newspaper: "You know about the proposal? Yes they are engaged.
"My future son-in-law is a really nice guy, really down to earth.
My family all like him. The good spirit is there."
Alfonso, 52, says he first met Lewis last year after the couple spent a week with him and his family on the Hawaiian island of Oahu and the sportsman left a good impression.
He said: "When he walked into the house for the first time he picked up one of the babies. That went down very well.
"He is sincere and he and my daughter seem genuinely happy together. Lewis is a really good guy. When they came to visit, we hired them a Jeep because he had never driven one before."
While a spokesman for 25-year-old Lewis refused to confirm their engagement, Nicole recently revealed how she wants to settle down and have children.
The 32-year-old singer said: "Do I see us getting married and having children? My head says yeah, but I'm really focused on my music now and I think that will come in time.
"I think I'll be really strict like my momma, maybe even worse. I won't let my children out of the house! I'll make them listen to classical music."
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