The Wales international, who has scored 18 tries for club and country this season, had already been named in the PRO12 Dream Team with half-back partner Dan Biggar and Ospreys captain Alun Wyn Jones for his efforts in helping the Welsh region reach the semi-finals.
The 26-year-old is the third Osprey to win the award, voted on by the 12 PRO12 club captains and vice-captains, succeeding last year’s winner Biggar, and Irish winger Tommy Bowe, who won the award in 2010.
Edinburgh scrum-half Sam Hidalgo-Clyne, 21, picked up the young player of the season title in his breakout season for the Scottish club that also saw him make his Scotland debut in the RBS 6 Nations in February.
Hidalgo-Clyne succeeds Glasgow Warriors lock Jonny Gray and is in good company with fellow Scots Stuart Hogg and Tim Visser also among the previous recipients of the award.
“I didn’t expect to be in the position that I am at the start of the season,” Hidalgo-Clyne told the PRO12 website.
“Going into pre-season you have got to earn your place and I tried to learn as much as I could off Greig before he left and take that into this season.
“On a personal level it couldn’t have gone much better.”
The coach of the season award went to Glasgow Warriors head coach Gregor Townsend, after he steered the Scottish club to finish top of the table, which secured a second home semi-final in a row.
“It’s great that it was voted by the other coaches in the league and I thank them for thinking of me, but because we are in a semi-final and the focus is on these next two games, I’ve not really reflected on it too much,” Townsend said.
“Really the award is what the club has done, it’s what the coaching team around me has done and ultimately what the players do week to week.”
There was further recognition for Scotland at the awards ceremony at the Guinness Storehouse in Dublin as retiring Glasgow Warriors captain Al Kellock received the chairman’s award in recognition of his outstanding service to the development of Glasgow and Scottish rugby, his performances and service to his country, the tournament as a whole and the game of rugby union.
While the Warriors also collected the Rhino collision kings award for their efficiency at the breakdown and tackling, judged by a panel of experts.
Ulster’s Craig Gilroy won the Sky Sports try of the year award for his score against the Scarlets after polling over 60 per cent of the public vote ahead of Munster’s Jack O’Donoghue.
After a disappointing season that saw Leinster miss out on the play-offs for the first time and saw none of their star names make the PRO12 dream team, Irish outside-half Ian Madigan won Rhino golden boot award with 87.04 per cent (47 kicks out of 54) ahead of Biggar on 86.96 per cent (60 kicks out of 69).
Connacht also received a boost as they picked up the SpecSavers fair play award, giving them £10,000 to put towards youth development.
Guinness PRO12 Dream Team: Liam Williams (Scarlets); Tommy Seymour (Glasgow Warriors), Robbie Henshaw (Connacht), Peter Horne (Glasgow Warriors), Craig Gilroy (Ulster Rugby); Dan Biggar (Ospreys), Rhys Webb (Ospreys); Denis Buckley (Connacht), Rory Best (Ulster Rugby), WP Nel (Edinburgh), Alun-Wyn Jones (Ospreys, captain), Franco van der Merwe (Ulster), CJ Stander (Munster), Tommy O’Donnell (Munster), Josh Strauss (Glasgow Warriors).
Players’ Player of the Season: Rhys Webb (Ospreys)
Young Player of the Season: Sam Hidalgo-Clyne (Edinburgh)
Coach of the Season: Gregor Townsend (Glasgow Warriors)
Chairman’s Award: Alastair Kellock (Glasgow Warriors)
Sky Sports Try of the Season: Craig Gilroy (Ulster Rugby)
Rhino Golden Boot: Ian Madigan (Leinster)
Rhino Collision Kings: Glasgow Warriors
Specsavers Fairplay Award: Connacht
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