Last night (February 21) saw Liam perform Oasis classic "Live Forever" as part of a tribute to the victims of last year's Manchester bombings.
Grande later posted on her Instagram story a video of Gallagher performing the tribute and remembering the 22 lives lost in the bombing, which took place outside Manchester Arena on May 22.
However, she was ordered by her doctors not to fly to the London, England-based awards show due to her illness. Gallagher was quickly snapped up as the replacement.
Gallagher, 45, was among the many musicians to perform in the benefit gig a year ago and his duet with Coldplay's Chris Martin on Oasis classic Live Forever was one of the highlights of the evening.
NME has asked Grande's camp for a direct quote.
The former Oasis man was drafted in at the last minute after Ariana herself was forced to cancel at short notice.
A source said: "Ariana desperately wanted to come - she was so ill but she still wanted to get on the plane".
"It will be the biggest talking point of the night", an insider told them. "It's a flawless choice". After the tragedy, Ariana organized the star-studded One Love Manchester concert, which raised money for the victims. "It's going to be the moment of the evening".
This isn't the first time that Liam has shown solidarity with his home city since the devastating terror attack.
The tribute to the 22 people who lost their lives and the more than 500 who were injured in the terror attack is reportedly set to be the centrepiece of the awards bash.