"Prenups may not seem particularly romantic but in the US they're incredibly common and Nicola's family all have agreements in place with their partners," a source said, quoted by The Sun.
"Brooklyn and Nicola's decision to go legal was entirely mutual," the source added.
"He's had experiences of girls desperate to get in on the Beckham name so they're delighted Nicola loves Brooklyn for him.
"And, of course, she doesn't need his money and has her own successful career."
According to the source, the prenup has already been signed by both of them.
"It's not complicated. Basically, in the unlikely event of a split, both parties will leave the marriage with what they put into it," the source explained.
"This includes assets and properties. Money will not change hands."
The couple met in 2017 at the Coachella music festival in the US.
They announced their engagement in July this year.
The couple will reportedly have two weddings one in the Cotswolds where the Beckhams own a home, and one in Florida where Nelson Peltz lives.
