Republic of Ireland winger Jonny Hayes will sign for Celtic after Aberdeen accepted a £1.3 million bid plus Ryan Christie on a season-long loan.
In a traumatic day for Aberdeen fans, Hayes switch to the treble winners was confirmed.
Hayes departure was confirmed just an hour after the Dons revealed an agreement had been reached on a compensation package to let boss Derek McInnes begin talks with Sunderland.
Hayes is currently on a family holiday and will be paraded at Parkhead when he returns.
The winger still had two years left on his Pittodrie contract having signed an extension in February.
The Dubliner had also been targeted by Championship clubs Cardiff City and Birmingham.
Cardiff had tabled a £1.2m bid but pulled out as they could not compete with Celtic’s player plus cash offer.
Now, Celtic boss Brendan Rodgers has won his battle to secure the 29-year-old.
Aberdeen vice chairman George Yule said: “It had been commonly accepted that Jonny, being 30 on his birthday and where he wants to play, will move on.”
Aberdeen had fought off interest for Hayes from Cardiff in January and knocked back three separate bids with the highest £650,000.
Having won that battle Hayes then signed on for an extra year until 2019 – a move that upped his value for the Dons should a club come calling again.
This time Aberdeen could not win the fight to retain the winger, who was shortlisted for the PFA Scotland Player of the Year award.
It was the second successive season Hayes had been in the four-man running for the prestigious award.
Aberdeen’s recently-appointed non- executive director Dave Cormack said: “If a player, Jonny or anyone else, has their mind working elsewhere we have to deal with that.
“However, that puts us in a strong position, it is only going to happen if it is right for Aberdeen.
“Whether that is other players coming as part of the deal or it is the right amount of cash for us.”
Hayes is the latest player to leave Aberdeen following the exit of former skipper Ryan Jack to Rangers, with Northern Ireland international Niall McGinn also rejecting a new deal.
Peter Pawlett turned down a new Dons contract to join MK Dons and Ash Taylor has also left.
Boss McInnes had targeted Birmingham City striker Greg Stewart as a summer window signing.
Stewart still has two years left on his Birmingham deal but boss Harry Redknapp is willing to let him leave this summer.
Hearts and Hibs have also targeted Stewart.
With Hayes leaving and McInnes exit imminent, the immediate task of the next manager will be to draft in players — and quickly. The Dons kick off the season in the Europa League second qualifying round on July 13.