Passage: In November 1913, Tagore learned he had won that year's Nobel Prize in Literature: the Swedish Academy appreciated the idealistic—and for Westerners—accessible nature of a small body of his translated material focused on the 1912 Gitanjali: Song Offerings. He was awarded a knighthood by King George V in the 1915 Birthday Honours, but Tagore renounced it after the 1919 Jallianwala Bagh massacre. Renouncing the knighthood, Tagore wrote in a letter addressed to Lord Chelmsford, the then British Viceroy of India, "The disproportionate severity of the punishments inflicted upon the unfortunate people and the methods of carrying them out, we are convinced, are without parallel in the history of civilised governments...The time has come when badges of honour make our shame glaring in their incongruous context of humiliation, and I for my part wish to stand, shorn of all special distinctions, by the side of my country men.”In 1921, Tagore and agricultural economist Leonard Elmhirst set up the "Institute for Rural Reconstruction", later renamed Shriniketan or "Abode of Welfare", in Surul, a village near the ashram. With it, Tagore sought to moderate Gandhi's Swaraj protests, which he occasionally blamed for British India's perceived mental — and thus ultimately colonial — decline. He sought aid from donors, officials, and scholars worldwide to "free village[s] from the shackles of helplessness and ignorance" by "vitalis[ing] knowledge". In the early 1930s he targeted ambient "abnormal caste consciousness" and untouchability. He lectured against these, he penned Dalit heroes for his poems and his dramas, and he campaigned—successfully—to open Guruvayoor Temple to Dalits.

Question: When did Tagore renounce his knighthood?
after the 1919 Jallianwala Bagh massacre