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The couple, who met and got engaged on the ABC reality show last year, explained that they do not necessarily want to wait until they are married before starting a family.
"The order doesn't matter," Rosenbaum told In Touch Weekly.
He continued: "[Ashley will] be the best mum ever. She's very maternal. And I know she'll be the softy; I'll have to be the bad guy!"
Rosenbaum also revealed that he is hoping for two children, while Hebert admitted that she would like one.
However, she joked: "Maybe we'll have one and a half!"
Last month, rumours claimed that Hebert and Rosenbaum will marry in the fall in a televised ceremony.
