The business school graduate, 31, has been vocal about not wanting to have children or start a family, while other half Heidi, 28, has made it clear she's ready to take that next step in their relationship.
Spencer and Heidi were so conflicted about the issue they even signed up for US reality show Marriage Boot Camp to confront it head on.
And now, after experiencing Boot Camp, Spencer says he's ready, and more importantly, wants to have kids.
"We've come to a place where I do want children," he told America's Today.
"We have a timeline now..."
That prompted Heidi to intervene and say she wanted their timeline to have children pushed up!
The couple - who married in 2009 - agreed that going on the WE tv reality show had been a good experience for them, although Spencer admits he'd completely underestimated what it would involve.
"I was hoping it would be a TV thing like, 'I signed up for a reality show, this will be fun!' It was a therapy nightmare. It was so intense. They're on you at six am shouting, 'Wake up! Boot camp!' Yelling all the time..."
Heidi added: "I think it was really hard going through it and really intense for us. We've come so far since The Hills in those days, and we've grown and learned, but they try to push you back into that mentality and try to push your buttons and set your trigger. So it was really hard for us but I think it was good."
The former MTV stars decided to sign up for the show as the issue of children had been raised several times during their marriage and they'd never been able to make an agreement.
"We've been trying to come to a compromise and talk about it," said Heidi. "But we weren't getting anywhere. It's hard when you're in one place in your relationship for years and you take that big jump, so I wanted to do it in a healthy, loving way but it wasn't quite going that way."
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