Mario Lopez doesn't hold back in his new memoir.

"When a man turns 40, it's an important time to pause and reflect on how he got there, and to make a mature plan for the future, and what better way than to write it down?" the "Saved by the Bell" alum told the "Ellen DeGeneres Show" in an interview airing today.

"When I decided I was going to do something like this, I just said, 'Alright, I'm going to be unfiltered and just put everything out there,'" he said about the book, "Just Between Us."

And, boy, did he. The 40-year-old "Extra" host shared one juicy tidbit from the book about his father, Mario Lopez, Sr.

"I was born in Chula Vista, [California], which is the border town to Tijuana, and I'm a child of immigrants," the Mexican-American actor told DeGeneres. "My dad did what he had to do to take care of us. Oftentimes when we'd take little trips across the border - and this was obviously pre-9/11 - we'd come back right away. He'd pull over and he'd open the trunk and sometimes people would come out."

Watch: Mario Lopez Talk About His New Autobiography

Related: 25 Things You Never Knew About 'Saved by the Bell'

Added Lopez, "I was like, 'Alright.' I didn't think much of it as a kid. Then, as I got older, it kinda dawned on me."

That led DeGeneres to joke, "At first, you just thought you had the better seat."

The talk show host then tried to get Lopez to open up about a romantic encounter he wrote about. In the book, Lopez revealed that he had a one-night stand with a major pop star but refused to name names.

Watch what happened when DeGeneres tried to guess who it is.