This Morning's Holly Willoughby stepped in McPartlin's absence for I'm a Celebrity, which still proved to be a ratings success in his absence.
He took part in the pre-recorded part of last year's series Britain's Got Talent, but Donnelly hosted the live shows alone.
It was the first time the infamous duo had been together for work since Ant took a break from the limelight following his drink-driving arrest previous year.
Welcoming his co-presenter back, Dec told the crowds at London Palladium: "We've got the judges back, the golden buzzer is back, and someone else is back".
Dec welcomed him with a big hug, after Ant's year-long break form presenting.
"My co-host for this series, would you please welcome - Mr Ant McPartlin!".
"Oh god, I'm really, really emotional now".More news: Four Civilians Shot As Zimbabweans Protest 150% Hike In Fuel Price
McPartlin will follow-up returning to Britain's Got Talent with work on Saturday Night Takeaway and I'm A Celeb, both of which are expected to return later in the year. "I've missed you all". Thank you very much, what a warm welcome. What a great show to come back to.
While Ant will be returning to Britain's Got Talent, his ex-wife Lisa Armstrong has been axed from her makeup job on the show.
"Ant welcome back. We missed you, it wasn't the same".
ITV has confirmed that filming for Britain's Got Talent 2019 started today (Friday, January 18), meaning the start date of BGT 2019 is imminent. I mean, even though Dec was brilliant, it still wasn't the same. "Can't wait to see you back on TV soon", posted a second.
The incident saw McPartlin put his career on pause having previously checked into rehab back in 2017 with a painkiller addiction.
He was driving while more than twice the legal drink-drive limit.