But the sharp-tongued Brit couldn’t resist poking fun at the 20-year-old singer, saying she is “really, really annoying.”
“I couldn’t be happier that Demi wants to come back this year,” Simon said after Fox made the announcement Thursday.
“She’s a superstar in her own right and was a fantastic mentor last year.
“Even though she can be really, really annoying - I truly enjoyed working with her and so did the artists.”
Demi gushed: “I am so excited to return as a judge and mentor on The X Factor.
“Last season was an unbelievable experience and I really enjoyed developing personal relationships with the contestants and the panel.”
Yet in February Demi told Cosmo On Campus that she thinks she agreed to appear on The X Factor too soon after receiving treatment for bulimia and bipolar.
She told the magazine: “I don’t think I was ready when I started The X Factor. In an ideal situation I would have maybe waited a year or more.
“I dived into work really quickly and maybe that wasn’t the best idea at the time…”