At his July 17 Kew Gardens gig in London, Elvis Costello introduced two of his stepbrothers, Ronan and Ruairi MacManus, to harmonise with him on the songs Oliver's Army and My Brave Face.
Kieran, Liam, Ronan and Ruairi MacManus, Costello's four half-brothers from his father's second marriage, formed the band Riverway in 2001. The band broke up in 2005 but the four have continued playing music.
The London Evening Standard reports that Costello said: "It's the first time we've been scheduled together.
"It is curious and it is probably the closest to the home parish that any of us could imagine."
The young Elvis Costello - aka Declan MacManus - was reared in nearby Twickenham, the son of Ross MacManus, a band leader and musician who played with the Joe Loss Orchestra among others. His mother Lilian sold records.
Costello and his step-brothers have become quite close since their father's death three years ago. Costello signalled their "common musical ground - it's just inherited".
He said: "Often when people are related to each other, when you harmonise there's a kind of spooky thing that happens. We didn't grow up together as kids and had never sung together but when I heard Ruairi, he sounded uncannily like me on my early records."
"It was different from my friends' dads," said Costello of growing up the son of a professional touring musician. "Exactly when their dads were coming home, dad went to work. I think being around music when you're a kid makes it ordinary and exceptional at the same time."
Fifty-nine-year-old Costello made his first public appearance in a folk club in the basement of St Elizabeth's Catholic Church in nearby Richmond as a teenager.