The 67-year-old Queen guitarist has praised the former 'American Idol' contestant - who has collaborated with Brian and drummer Roger Taylor since 2011 - by saying his vocal ability is enough to challenge the band's late frontman, Freddie Mercury.
He said: ''They're difficult songs to sing, Queen songs. There's too much range. So many people can't sing them in the original key -- even if they are good singers, Adam comes along, [and] he can do it easy. He can do it in his sleep! He can sing higher than even Freddie could in a live situation.''
The 'Don't Stop Me Now' hitmaker admitted Freddie - who died of bronchopneumonia brought on by AIDS in 1991 - may even feel peeved the star's singing ability lives up to his legacy.
He continued: ''So I think Freddie would look at this guy and think, 'Hmm... Yeah. Okay.' There would be a kind of, 'Hmm ... You bastard. You can do this.'''
The musician also complimented Adam, 32, for his expert showmanship when on stage, which is exciting while not being a copy of the former lead singer's behaviour.
Speaking to Japan's Universal Music, he added: ''He doesn't have to try. He is a natural, in the same way that Freddie was.
''We didn't look for this guy, [but] suddenly he's there, and he can sing all of those lines. ... He doesn't imitate; he just does his own thing.''
'Smalls Change (Meditations Upon Ageing)' arrives in April.
The two awards have made for a great 72nd birthday present for the country music icon.