Top Gear host Matt LeBlanc, the former Friends favourite Joey, gate-crashed a wedding during filming for a new show.He surprised a bride and groom and their wedding guests at St Paul's Cathedral as he and professional rally driver Ken Block drove past.LeBlanc stuck his arm out of the car window to wave as the pair were being filmed driving around the streets of London in Block's 623.7kW 4WD Hoonicorn Mustang, which took them over London's Tower Bridge, where they snapped a picture using a selfie stick.American actor LeBlanc is apparently still unfamiliar with London. He was pictured clutching a guide book to London as he navigated the unfamiliar streets with Block at the wheel.Filming for the Top Gear reboot is well under way, with the launch of the new series on BBC2 due to start in May.A seven-strong lineup includes LeBlanc, radio DJ and presenter Chris Evans and Top Gear stalwart The Stig.Formula 1 commentator Eddie Jordan, German racing driver Sabine Schmitz, motoring scribe Chris Harris and car reviewer Rory Reid are also on boardIts previous incarnation, starring Jeremy Clarkson, Richard Hammond and James May, was one of the BBC's most popular exports.Under Clarkson, May and Hammond, it was watched by an estimated 350 million people in 214 territories earning a reported £50m a year. ..