Written (by Terry Cashman) and first recorded (as a demo) by Cashman, Pistilli & West (1967, released 1968).
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. Cashman sent his demo to Lou Adler at Dunhill Records, with the hope that The Mamas & The Papas would record the song, and recalls: ‘Adler saying ‘Hey, this is a great song.’ But John Philips is doing mostly his own songs right now. So, okay, fine. The Left Banke sounded to me also like a group that could do this song, but they passed on it. And then with nobody in mind I went to a producer named Jerry Ross, who was a very hot producer (‘Apples, Peaches, Pumpkin Pie‘, ‘98.6’).