A new album, The Royal Philharmonic Orchestra Plays Prog Rock Classics includes a version of Focus II with Van Leer on flute. Worth a listen.
Looking at the music of Dutch rock band Focus, started in the late sixties by Thijs Van Leer (b /31/03/48) with Jan Akkerman (b 24/12/46). Van Leer still performs and records under the name today (official site here). Akkerman's site here.