Nick and Vanessa Lachey used to look through each other's phones.

Nick and Vanessa Lachey used to look through each other's phones

Nick and Vanessa Lachey used to look through each other's phones

The 48-year-old star and Vanessa, 41, revealed during the reunion episode of 'The Ultimatum: Marry or Move On' that they used to secretly spy on each other.

Speaking about contestant April's decision to look through her partner's phone, Vanessa confessed: "You being The Ultimatum detective, April, decided to go through Jake's phone when he was sleeping.

"So I've got mixed feelings about that ... I know there was a time in my life when I did it."

Nick - who co-hosts the show with his wife - then said: "You wait, what?"

Vanessa then told Nick that she knew he'd gone through her phone, too.

She shared: "You did it too! I'm actually really surprised you figured out my password that was a good one."

Meanwhile, Nick was married to pop star Jessica Simpson between 2002 and 2006.

And in spite of their split, the blonde beauty previously insisted that she'll always remain respectful of her ex-husband.

Jessica - who has Birdie, three, Ace, eight, and Maxwell, nine, with her husband Eric Johnson - said: "I was really young and my success hadn't really begun.

"He knew me as this young, innocent 18 year old that had never been introduced to the world in so many ways. I went straight from my father to him.

"Nick's very smart. He was eight years older than me, but he was also young.

"We meant a lot to each other and we always will. I want to be very respectful because I married him for a reason and we were together for seven years for a reason.

"He has a family now and I would never say anything to disrespect that."