The 26-year-old has left the Scottish champions for Brighton.
Brighton confirmed Kayal's signing for an undisclosed fee recently, with the midfielder having been granted a work permit yesterday.
The move puts to an end five years at Celtic, during which Kayal won multiple trophies and made 131 appearances for the Bhoys.
The 26-year-old had fallen out of favour, however, under Ronny Deila this term - and will now turn out for Chris Hughton's men south of the border.
Kayal will not forget the support of the Celtic fans, though, and has shown as much with an emotional tribute to his now former supporters on Instagram after securing the move.
Along with a picture of himself in a Celtic shirt, Kayal's full Instagram message read:
"I would like to thank the Celtic fans for the tremendous support they gave me throughout my time with the club.
"They are amazing fans, committed to the team and they were incredibly supportive to me all through my time in Glasgow.
"Coming to a new country, that support was huge for me and I now have many great friends and good memories from my time playing in the famous green-and-white hoops.
"I will see them all soon. I will be back to watch Celtic in the future – as the club will always be in my heart – and I wish everybody at the club the very best for the future.
"For now it is time to begin a new chapter on my career with Brighton & Hove Albion, and I am very much looking forward to playing for the supporters here in Brighton."
Celtic currently sit top of the Scottish Premiership, also with a game in hand over second-placed Aberdeen. Brighton, meanwhile, struggled this season under Sami Hyypia, who resigned and was replaced by Hughton.
Now, Brighton sit 19th in the Championship, five points clear of the relegation zone.