Mary Lambert told MTV News that it was difficult to keep quiet about American Idol alum Jennifer Hudson's surprise performance at Sunday's Video Music Awards.

Hudson joined Macklemore & Ryan Lewis and guest vocalist Lambert during their live performance of the gay marriage anthem Same Love.

As Macklemore rapped, Hudson appeared from behind to sing the song's chorus performed on the single by Lambert: “And I can't change; even if I tried; even if I wanted to; my love she keeps me warm.”

Slowly Lambert made her way to the stage's forefront and took Hudson's hand.

“I'm not crying on Sundays,” they each belted out, a melodic hook Lambert earlier explained was a reference to her difficulty in reconciling being gay and Christian.

“That was cool,” Lambert told MTV News. “In rehearsals, I was like, 'How can I not talk about this? I have to keep my mouth shut.' It was really hard. [Hudson's] a phenomenal singer and a phenomenal person, performer – all of it.”

On the song's message, she added: “It's really incredible to be a part of such an incredible social movement and to have the support and to go around the world and say, 'What's up? I'm gay,' and have everyone's support. That is really cool.”

The video for Same Love also won the VMA for Best Video with a Social Message. (Watch the video in our video library.)

(Related: Macklemore says gay rights are human rights in accepting VMA award.)

Lambert earlier this week debuted the video to She Keeps Me Warm, which she described as “the other side of the Same Love story.” (Watch the video in our video library.)