The presenter has been on her summer break but will be hosting the ITV daytime programme on Monday (4 September) alongside Alison Hammond.
Willoughby used to present with Phillip Schofield but has not had a permanent co-host since he departed earlier this year amid a scandal that saw him admitting to having an “unwise but not illegal” affair with a much younger ITV staff member.
On Friday's show (1 September), presenters Andi Peters and Rochelle Humes announced that Willoughby was on her way back and that she would be joined by Hammond, who usually hosts the show with Dermot O'Leary.
While some viewers were pleased to hear that Willoughby was returning, others said they would miss stand in hosts such as Peters and Humes.
"Rochelle and Andy - great combo on #thismorning, so natural, sincere and funny," one posted on Twitter, adding: "Can we have more please?"
Another admitted Friday's show was the "last time" they would be watching and someone else agreed: "I won't be watching."
"So it's back to normal Monday but after enjoying Rochelle and Andi this week and absolutely enjoyed them so much, will not be watching the programme any more," said another.
Peters and Humes have been a popular pairing on This Morning this summer, and there have been calls to make them more permanent.
“Absolutely love love love this pair, brilliant and funny making the show so fresh again," one fan recently tweeted.
“Andi and Rochelle bring fresh air to the show,” said someone else.
“They need to be the new full time presenters.”
Watch: Michaela Strachan parodies Holly Willoughby's This Morning statement