The singer then launched into her 2007 hit "Gunpowder and Lead."
Lambert uploaded a photo collage of the sweet proposal to Instagram, writing, "I said YES! But he has to wait 25 years. This sweet boy Sebastian is a little gentleman. #pinkring #proposal #mademyday #jersey #spreadthelovetour."
One fan, Sarah Goddard, tells WHO that little Sebastian approached her at the concert after seeing her "meet-and-greet" sticker and asked Goddard to propose to Lambert for him.
"I told his mum he could come in with me 'as my son' so he could propose to Miranda himself," Goddard says.
"He bought the ring himself … his mom said he's been holding on to it since Christmas, waiting for an opportunity to propose to Miranda."
Lambert, who split from Blake Shelton last summer, has been dating Anderson East since last December.