Winning the league title and the FA Cup in the same season. Was once considered nearly impossible. Arsenal did it in 1971 and 1998 and 2002. United did it three times under Ferguson. The Treble (league, FA Cup, and Champions League) is even rarer and has only been done twice in England, by United in 1999 and City in 2023.
"1971: Arsenal clinch the league at White Hart Lane, then beat Liverpool at Wembley five days later. The Double, done the hard way."