Simons joins fellow contestants John Barrowmanm, Harry Redknapp, The Chase star Anne Hegerty, Coronation Street actress Sair Khan, DIY SOS presenter Nick Knowles, James McVey from pop band The Vamps, former X Factor contestant Fleur East, Inbetweeners actress Emily Atack and Malique Thompson-Dwyer from Hollyoaks.
Speaking ahead of the launch, Holly said: "I couldn't be more excited to have been asked to stand alongside Dec for the next jungle adventure".
I'm a Celebrity Get Me Out of Here returns shortly and the line-up for the hugely popular reality TV show has now been revealed. It was only a little one, but it was a real-life spider.
"He knows I'll look after the show and keep it warm for him".
"So no, I don't think doing this will be tougher", said the 71-year-old.
"I am scared of everything you have in there and I am scared of all the trials", she said. The buck stops with you.
For the first time, Dec will have a new co-host when "I'm A Celebrity" kicks off next week, with Holly Willoughby stepping into Ant's shoes as he continues his hiatus from television work.More news: Mahomes sets Chiefs single-season passing TD mark
More news: Stan Lee, creator of Spiderman comics, dies at 95
More news: Duterte skips ASEAN summit events
"I have been with Sandra for 54 years and I hate being away from her".
"But realistically, you know they are not going to do anything that hurts you", he added.
'I don't think I would have been able to do my job properly if I couldn't have seen them'.
He said: "Everyone has phobias and I am terrified of some of the things on the programme".
The long-standing I'm A Celeb duo of Ant and Dec will be torn apart for the first time.
"For me eating testicles is going to be the worst", said the 20-year-old actor.
Earlier this year, fan favourite Ant McPartlin was charged with drink-driving following a traffic collision.