Original: He made a notable exception when he took part in a concert of chamber music in the White House on November 13, 1961, at the invitation of President John F. Kennedy, whom he admired.
Simplified: He made one big exception to his decision not to visit Franco-friendly countries: in 1961 he took part in a concert of chamber music in the White House on 13 November where he played to President John F Kennedy whom he admired.