Alex Ferguson has led the tributes to outgoing Arsenal boss Arsene Wenger by calling the Frenchman "without doubt one of the greatest Premier League managers".
It was announced today that Wenger is to leave the Gunners next month after a near 22-year spell, during which time he won 10 major trophies, including three Premier League titles.
His Arsenal teams were regularly involved in title races with Ferguson's Manchester United and the Scot, who was at Old Trafford from 1986 to 2013, praised the 68-year-old.
"I am really happy for Arsene Wenger," Ferguson told ManUtd.com.
"I have great respect for him and for the job he has done at Arsenal.
"It is great testament to his talent, professionalism and determination that he has been able to dedicate 22 years of his life to a job that he loves.
"In an era where football managers sometimes only last one or two seasons, it shows what an achievement it is to serve that length of time at a club the size of Arsenal.
"I am pleased that he has announced he is leaving at this stage of the season, as he can now have the send-off that he truly deserves.
"He is, without doubt, one of the greatest Premier League managers and I am proud to have been a rival, a colleague and a friend to such a great man."
Wenger's greatest achievement for many was being at the helm of the 2003-04 'Invincibles', who won the league and went through an entire campaign unbeaten.
Thierry Henry, their top scorer that campaign, told Sky Sports: "His legacy is untouchable. Managers, fans from other teams - (they talk about) how Arsene changed Arsenal."
Henry's old team-mate and former Gunners skipper Tony Adams, who was captain of Wenger's double-winning sides in 1998 and 2002, wrote on Instagram: "Thanks for everything Arsene. Move over Herbert (Chapman), Arsene Wenger the greatest Arsenal Manager."
Defender Per Mertesacker admitted the news caught Wenger's current players by surprise and midfielder Jack Wilshere insisted the squad were determined to end his reign on a high as they target winning the Europa League.
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Wenger was seen as a trailblazer for foreign coaches and Liverpool boss Jurgen Klopp said he was "always a big role model".
David Seaman, Wenger's first-choice goalkeeper for the two doubles, admitted he was pleased the Arsenal boss was departing on his own terms rather than being axed or forced out by fans disappointed with their recent struggles.
"The fans that are celebrating like they've won the lottery, it makes me a little bit angry if I'm honest," Seaman told talkSPORT.
"It's time to show respect and realise what he's done. For me, he is Arsenal, and it's right that he's decided to leave on his own terms."
Current United boss Jose Mourinho, who has had numerous run-ins with Wenger, once calling him " a specialist in failure".
Today, however, he said that he had great respect for the Arsenal manager and hopes that he does not now retire.
"I know what it means: (he won) three Premier League titles, seven FA Cups, and not just that. What he did in Japan, in France. What he brought to the French football," Mourinho added.
"What he gave to Arsenal even in the period without Premier Leagues, all the transition of the club from stadium to stadium, everything he did."
Other ex-Arsenal players also expressed their gratitude to Wenger on social media. Chelsea midfielder Cesc Fabregas described the Frenchman as "like a father figure to me" on his Instagram account, while Robin van Persie called Wenger "Definitely one of the very best ever!" on Twitter.
Wenger is far and away the longest-serving boss across England's top four divisions and League Managers' Association chairman Howard Wilkinson lauded his impact on these shores.
"Arsene Wenger is without question one of the most significant managers to have graced the game of professional football here in England," Wilkinson said.
"From his arrival at Arsenal, it was patently clear that here was someone with tremendous foresight, fortitude and imagination.
"A man of high principles, he was never prepared to compromise his beliefs and, in so doing, he enhanced the history and reputation of one of the world's great clubs."