The former Fifth Harmony band member appeared on Britain's This Morning Wednesday and opened up about her conversation with Grande after the explosion at her concert that killed 22 people and injured more than 50.
"Yeah, I spoke to her after that happened," Cabello said as her face dropped. "I'm so sorry, I can't even imagine."
When asked how Grande sounded on the phone, the singer added, "[She was] so shaken up. I mean, what can you say?"
On Tuesday, the "Side to Side" singer announced she will be hosting a Manchester tribute concert to benefit the victims and families affected by the terror attack—a move Cabello praises and supports.
"We were just talking in the car about the concert. I'm super proud of her, coming back to Manchester," the singer said. "Ariana is one person who has always been so supportive of me."
The "One Love Manchester" benefit concert will take place at the Emirates Old Trafford Cricket Ground on June 4 and will feature some major names, including Justin Bieber, Coldplay, Miley Cyrus, Niall Horan, Katy Perry, Take That, Usher, Pharrell Williams and more.
Tickets will go on sale Thursday, June 1, at 10 a.m. B.S.T., but fans who attended Grande's Manchester concert on May 22 will be able to register for free tickets to attend the benefit. It will also be broadcast on BBC Television as well as on BBC Radio and Capital Radio Networks, and it will also be streamed with a digital partner worldwide (to be announced soon).
All proceeds from the show will go towards the We Love Manchester Emergency Fund set up by the Manchester City Council in partnership with the British Red Cross. It will support people who have been injured or bereaved by the Manchester attack last week.