The pair reunited to host the ITV daytime show - which saw co-host Phillip Schofield quit earlier this year following the revelations of his secret affair with a much younger male colleague - after the summer break with an opening performance from the stars of O2 show Mamma Mia! The Party.
Willoughby, 42, and Hammond, 48, danced onto screen and shimmied together to the Abba hit.
Willoughby then told viewers: "What a start to the show. It's so good to see you all. We are back from our summer break.
"With a new season comes new adventures."
This was followed by a reel of new segments coming up on This Morning in the autumn.
The presenters were then shown back in the studio with new cushions on the sofa.
As they introduced what was coming up on the show, including the return of competition Spin To Win, Hammond: "I've got something to tell you Holly. No balls."
Willoughby asked: "What happened to my balls over the summer?"
Hammond said: "They were so dry. We got rid of your balls. It's called Spin To Win."
In the competition segment selected callers could previously choose between spinning the wheel — traditionally operated by Schofield — or Willoughby selecting a bingo-style ball which would allocate the size of their prize money.
Willoughby — who is mother to three children Harry, 14, Belle, 12, and Chester, eight — usually takes a six week break from the show during the school summer holidays.
This year she began her break two weeks earlier, with no prior notice to viewers, last appearing on the sofa on Thursday, 6 July.
She also took a two week break form the show in May after Schofield announced he was was stepping down from the show after 21 years.
When she returned to the show she addressed the revelations of Schofield's affair, saying she felt "shaken, troubled and let down".
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