They won the league at Tynecastle - and one pundit reckons that the Celtic party afterwards must have been bouncing if recent results are to go by.
Since winning the Premiership trophy in their first post-split game against Hearts, Ange Postecoglou's champions have lost to Rangers and Hibs, and drew with Mirren at home ahead of Saturday's trophy day game against Aberdeen. The Hoops' boss has taken the flack and put recent performances down largely to rotation, the likes of third-choice goalkeeper Scott Bain played in the 4-2 loss at Easter Road, and making errors that resulted in goals.
Former Celtic defender Mark Wilson wonders if the party started in Edinburgh has had a lingering hangover effect, as a date with Treble destiny looms in the Scottish Cup final against Inverness Caley Thistle. The periphery men have been told to shape up, as Wilson told Sky Sports: "It must have been some party at Tynecastle when they won the league because after that, there is no doubt the foot has come off the pedal.
"That is a number of things. The manager has changed the team, allowed more games for guys who have sat on the bench or in the stand for a lot of the season.
"So there is food for thought for Ange Postecoglou in the summer. They are going for a Treble but the Celtic manager will be thinking about how he strengthens an already very good side.
"It didn't look good when the goals squirmed past him (Bain). What we have seen is the gap between those fringe players and the players Age Postecoglou has depended on and who have delivered week after week.
"Although he can revel on what has gone on in the past and the Scottish Cup final to come, but come July, he will be thinking who he gets in to replace some of those fringe players."