"had had had had had had had had had had had" had previously been the longest consecutive repetition of a single word in a grammatically acceptable sentence. That record has now been broken (etc.)
Based on this we can now also say: "The record for the longest consecutive repetition of a single word was previously held by had had had had had had had had had had had; had had had had had had had had had had had had is now the record holder" etc etc
James while John had had had had had had had had had had had a better effect on the teacher
https://en.wikipedia.org/wiki/James_while_John_had_had_had_had_had_had_had_had_had_had_had_a_better_effect_on_the_teacher