Oh God, I'm really emotional now.
McPartlin, 43, stepped away from his TV roles last March after a drink-driving charge. "I've missed you all".
He then pointed at Dec, saying: "I've missed you". Get Me Out Of Here! - with Holly Willoughby taking his place. The 42-year-old liked a tweet from a fan that read: "For you to lose your job because of your ex is very unfair and unjust, you're a handsome soul".
The audience fell into a wild cheer as Ant walked onto the stage, before he added: "Hello everyone".
Another said: "Nice to have you back Ant. Dec is great and all that but we all know you're the amusing one".
While the audition process for Britain's Got Talent will begin this month, the show is not due to air on ITV until springtime this year.
Aiia Maasarwe's father joins hundreds of mourners in silent vigil
Vice-chancellor John Dewar addressed the emotional crowds, announcing that security for students would be ramped up. She had been out at a comedy show, 9News reports, and was taking a tram as she spoke on the phone with her sister.
Dec subsequently presented I'm A Celebrity. It would be like me not being with David (Walliams), I would be happy, but not happy - if that makes sense.
Ant and Dec at the NTAs in 2018.
He was later banned from the road for 20 months and fined £86,000 for driving while more than twice the legal drink-drive limit.
Another post read: "Great to see you both back on the scene - together".
On Friday, Ant was reunited with his usual co-host Declan Donnelly, after a long period out of the spotlight, following his arrest and subsequent conviction for drink-driving last March.
McPartlin, who divorced wife Lisa last year, previously struggled with a two-year addiction to super-strength painkillers following a knee operation.
Simon and Amanda have been the judges of every season of Britain's Got Talent, while David and Alesha have been on the show since season six in 2012.