Ronnie Wood congratulated former Faces lead singer Rod Stewart on the news he and his wife Penny Lancaster were expecting another baby at the band's first reunion concert.
Simply Red singer Mick Hucknall replaced Rod, who chose not to rejoin the band at Wednesday night's gig.
Many fans of the 1970s rock group, known for hits such as Stay With Me and I'd Rather Go Blind, expressed surprise at the decision to bring in Mick as lead singer but he managed to win over the crowd.
Kicking off their reunion tour at a concert held by American Express at the British Music Experience at London's O2 Arena, Mick ran through the hits to rapturous applause and shouts of "best band in the world" from the crowd.
Playing to an audience of 400 people, it was an intimate gig for lead guitarist Ronnie, who went on to play for The Rolling Stones when Faces split up in 1975.
Ronnie congratulated Rod on the news he was to become a father again.
"Good luck to him, he's a great dad," he said.
Speaking before their performance, the rocker said it was "magic" having Mick sing with the band.
He said: "We do miss Rod but having Mick here is just unbelievable because it's one of those situations that you probably at first think wouldn't work but it's magic."
Mick, who is 15 years Rod's junior, added: "I wanted to be Rod when I was 12, who wouldn't? He's one of the greatest rock icons and we'll honour him tonight. But if he isn't doing it and someone else gets the chance to do it who's a fan, then why not?"