Horvat has worn 53 his entire professional career, dating back to his OHL entry draft. He was drafted by the London Knights, alongside good friend Ian Jenkins. Jenkins was killed in a car accident only a few weeks later.
GM Lou Lamoriello has a rule where no player can wear a number above 40, barring players that were grandfathered in. As for Horvat, he would most likely look to choose another number with significance to him, but he was limited to just a few numbers left under 40.
He ended up with 14, which will hopefully bring new good memories, but it will never have the significance that 53 brought.