In 1887, the British Empire celebrated Victoria's Golden Jubilee. Victoria marked the fiftieth anniversary of her accession on 20 June with a banquet to which 50 kings and princes were invited. The following day, she participated in a procession and attended a thanksgiving service in Westminster Abbey. By this time, Victoria was once again extremely popular. Two days later on 23 June, she engaged two Indian Muslims as waiters, one of whom was Abdul Karim. He was soon promoted to "Munshi": teaching her Hindustani, and acting as a clerk. Her family and retainers were appalled, and accused Abdul Karim of spying for the Muslim Patriotic League, and biasing the Queen against the Hindus. Equerry Frederick Ponsonby (the son of Sir Henry) discovered that the Munshi had lied about his parentage, and reported to Lord Elgin, Viceroy of India, "the Munshi occupies very much the same position as John Brown used to do." Victoria dismissed their complaints as racial prejudice. Abdul Karim remained in her service until he returned to India with a pension on her death.
Who discovered that Karim had lied about his parentage to Victoria?  (If the question is unanswerable, say "unanswerable")
Equerry Frederick Ponsonby