In an interview with TV Guide, the 'Womanizer' singer credited Lovato with helping her to "toughen up" when dealing with contestants on the Fox singing competition.
"She's a very good judge. She toughens me up! Sometimes I listen to [her] and I'm like, 'Oh, God, I've got to be a little stronger'," Spears said.
"Even though she's really young, she has such a sophistication about her. She's cooler than me."
Lovato also had positive things to say about Spears, adding: "I've said from day one, when [Britney] stepped on set, how funny she is. I don't think a lot of people have gotten to see her personality and her sense of humour."
Former American Idol judge Jennifer Lopez recently offered Spears advice for her X Factor judging role, saying that the star should "be herself".
Watch a promo for the upcoming season of The X Factor USA below: