Jessica Simpson and fiance Eric Johnson will sign a prenuptial agreement

The couple ' who announced their engagement in November after just six months of dating ' have been discussing their options and will agree to a legal deal over their assets before they tie the knot.

A source said: "There will definitely be a prenup. Jessica has said she wants one. Jessica and Eric have talked about it.

"Eric understands that there needs to be a prenup. He's supportive of it."

Singer-and-actress Jessica is said to be worth $750 million and former NFL star Eric wants to show he's not after her money.

The source added to Us Weekly magazine: "He really loves her. He's a low-key guy. He's not into the glitz and materialism of Hollywood at all."

While the couple ' who have both been married before - are signing a pre-nuptial agreement, they are planning their future together and want to start a family.

Jessica said: "I definitely see myself having a family with Eric, so that's exciting to think about."

Speaking about her husband-to-be, the blonde beauty gushed: "Every day is a romantic day with him. I'm very blessed."

Jessica was previously married to singer Nick Lachey while Eric's five-year marriage to wife Keri Johnson was officially ended earlier this year.