Paris Hilton reveals from where she learnt her catchphrase 'that's hot'

Even though Paris Hilton has switched to "sliving," "that's hot" will always be associated with her name.

However, the 42-year-old heiress claims in her most recent book Paris: The Memoir that she actually learned the expression from her younger sister Nicky Hilton while she was in middle school.

"At some point, I heard Nicky say 'That's hot,' and it resonated with me," the Stars Are Blind  singer noted.

"I wrote it in my diary and doodled flowers and fireworks around it. It's such a great statement, isn't it? Positive. Unpretentious. The word hot is evocative; there's energy in it."

Hilton saw "That's hot" as "a little positive affirmation."

"Suddenly there seemed to be a lot of things in my world that deserved this little accolade, and I recorded them faithfully in my diary," she wrote. "Mom got me markers with glitter in them. That's hot. We learned how to diagram sentences. That's hot. Nicole [Richie] is sleeping over the whole weekend. That's hot."

Before Hilton popularised the expression, it gained traction at her school.

"Pretty soon all the kids in my class were saying, 'That's hot,'" the mom of newborn son Phoenix penned in her memoir. "Like I made 'fetch' happen!"

After season 2 of The Simple Life, Hilton decided to trademark "That's hot."

"I wasn't sure what I wanted to do with it; I only knew I didn't want anyone else to get there first," the businesswoman writes.