A personal letter penned by Queen Elizabeth II more than six decades ago has surfaced, offering a rare glimpse into the late monarch's joy following the arrival of her youngest child.Written at Buckingham Palace on April 1 1964, the two-page correspondence was addressed to Marion Stein, Countess of Harewood, a close friend of the Queen.In the letter, Elizabeth II shared that Prince Edward, then just three weeks old, was "flourishing" and express…