By the way

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Across
  1. 2. Athlete with most Olympic gold medals
  2. 4. F1 constructor with most Constructors’ titles
  3. 6. Composer of The Four Seasons
  4. 8. Actor who played Jack Dawson in Titanic
  5. 10. Genre born in New Orleans around 1900
  6. 12. Most-followed person on Instagram
  7. 13. Nintendo franchise with Mario and Luigi
  8. 15. Band behind Abbey Road album
  9. 17. Club with most UEFA Champions League titles
  10. 19. King of Pop
  11. 21. Series featuring the Iron Throne
Down
  1. 1. Nation with most Rugby World Cup titles
  2. 3. 2020 Oscar Best Picture winner
  3. 5. Only clay Grand Slam tournament
  4. 7. Social media platform with blue bird logo
  5. 9. Host city of the 2012 Olympics
  6. 11. Nation with most FIFA World Cup wins
  7. 14. Country with most World Cup final appearances
  8. 16. Queen of Pop
  9. 18. Highest-grossing film of all time
  10. 20. Instrument played by Yo-Yo Ma