Meanwhile, Keegan belted out: "Patience makes her heart grow stronger. Reassure her she's where I want to be!"
Keegan, of Whangaparaoa, was born at 26 weeks and was diagnosed with cerebral palsy when he was nine months old. He also suffers from epilepsy and autism.
Yesterday one of his biggest dreams came true thanks to the Make-A-Wish New Zealand organisation, which works to grant the wishes of young people with life-threatening medical conditions.
Keegan's dream was to record a song with a top rock band.
A keen musician and a big fan of rock music, he is one of 200 Kiwi youngsters whose dreams will come true through the organisation this year.
He said being able to sing alongside Opshop was something he still could not get his head around.
"I've been singing on stage for a very long time. I love music. It's about connecting with the song and letting go," he said.
"My favourite band is Queen and my favourite song is Love of My Life. Here, I'll sing it for you."
Keegan joked with members of the band and happily posed for rock-style pictures, stretching out his arms and showing his tongue.
At one point he bravely asked Bobby Kennedy: "So when did you decide to work for me?"
Keegan roared with laughter when Kennedy replied: "We're happy to do this. We heard you wanted Queen, but they weren't available, so here we are."
Kerrison said they were looking forward to recording a song with Keegan, which will be put on CD.
"It's just about hanging out with him and jamming with him. He loves music and that's us, too," Kerrison said.
The Make-A-Wish organisation has been working with children and young people for 26 years.
Chief executive Carolyn MacDonell said doing such things helped bring happiness to children who had suffered so much in their lives.
"It's an absolute privilege to grant wishes. We can see the excitement and the joy that it brings them and that's what it's all about."