Written (by Terry Cashman) and first recorded (as a demo) by Cashman, Pistilli & West (1967).
Hit version by Spanky and Our Gang (US #9/CAN #7 1967).
From the wiki: “‘Sunday Will Never Be the Same’ was written by Terry Cashman and Gene Pistilli, who, with Tommy West, recorded it for their debut album, Bound to Happen, in 1967. Hedging his bets, Cashman also sent a copy of the song to Lou Adler at Dunhill Records, with the hope that The Mamas & The Papas would record the song.
“Cashman recalls: ‘Adler saying ‘Hey, this is a great song.’ But John Philips was doing mostly his own songs [for the group] right now. So, okay, fine. The Left Banke sounded to me also like a group that could do this song, but they also passed on it. And then with nobody else in mind I went to a producer named Jerry Ross, who was [at that time] a very hot producer (‘Apples, Peaches, Pumpkin Pie‘, ‘98.6’).