“@britishbakeoff is back with a new series and addition - Meeeeee!!” Hammond posted.
“I can not wait. Coming soon to @channel4.”
Excited messages poured in from Hammond’s colleagues, with fellow This Morning presenter Holly Willoughby posting a string of hearts and raising hands emojis.
Carol Vorderman, who is also a regular on the ITV daytime show, said the role was “perfection”.
“You're the showstopper my babe,” she added, in a nod to one of the baking show’s rounds.
TV cook Juliet Sear chimed in: “Nice one Alison!!! I know you will really be AWESOME on this.
"I can’t wait to see you shine! Xxx.”
Denise Welch from Loose Women said that it was the “best casting ever”.
Welch’s fellow panellist Ruth Langsford wrote: “Can’t wait to see it….you’ll be BRILLIANT!”
“Can’t wait,” said singer and TV star Michelle Visage.
“Slay all day,” added chart star Paloma Faith.
Lucas stepped down from Bake Off in December last year after co-hosting the much-loved show for three series.
At the time he said it had been a “delicious” experience but that he was “cheerfully passing the baguette” onto someone else.
Watch: Dame Prue Leith is 'really glad' Alison Hammond is joining The Great British Bake Off