Celtic's January signing has been reflecting on the league title.
Indeed, on the Celtic squad's group chat, goalkeeper Gordon was the first to announce Aberdeen had lost to Dundee United, securing the league title for the Hoops.
And Mackay-Steven's reaction produced a 'strange feeling' for him, although the winger admitted it was also a 'nice' one.
The 24-year-old January signing told reporters: "I was watching the scores come in and we also have a group chat online between all the boys at Celtic, so it was a nice feeling to know we had won the league.
"I think it was Craig Gordon who first said we were the champions when the final whistle had gone and it was a strange feeling.
"It was nice that my old club did us a turn. For [Dundee] United to get the three points was a big thing and, hopefully, they can kick on until the end of the season."
Celtic's successful Scottish Premiership campaign continues on Sunday afternoon, when the Hoops travel to Aberdeen at 2.30pm. Their visit of the Dons could have been a title decider but Mackay-Steven's old side beat them to secure an earlier confirmation of the league trophy for Ronny Deila's men.
After facing Aberdeen, Celtic travel to St Johnstone and then host Inverness Caledonian Thistle.
Deila's team selection for the Bhoys will be interesting in the closing stages of the season. With the title wrapped up, will the Norwegian turn to some of his youngsters or perhaps guarantee more opportunities for those with uncertain futures at Parkhead?