Hilton has been dating the baseball player since earlier this year, following her split from rocker Benji Madden in late 2008.
The pair was recently rumored to be considering walking down the aisle.
And now Reinhardt has confirmed rumors of an imminent proposal -- insisting he will wed the hotel heiress.
He tells British newspaper the Mail on Sunday, "I am going to ask her to marry me but I can't say when. I don't want to ruin the surprise."
A source adds, "They have been dating for five months and Doug has already said he's going ask Paris to marry him in a couple of months. He doesn't see the point in waiting around. He will ask her to marry him this summer."
Hilton was previously engaged to model Jason Shaw before they split in 2003. She also broke off plans to wed Greek shipping heir Paris Latsis in 2005.
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