But he made very little impact on Tyneside and ended up leaving on a free transfer, despite being tipped as one of the best players to emerge from Hungary’s national pool seven years ago.
Three years on from his Newcastle exit Kadar is preparing to play at Euro 2016 after starring for Hungary in the play-offs this weekend.
We’ll never know if Kadar was cut out for life in the Premier League, but after two solid performances for Hungary against Norway in the Euro 2016 play-offs, it begs the question whether Newcastle let him go too early.
He had FIVE managers in four years, experience a dressing revolt after relegation, have his leg broken while challenging Jordan Henderson and narrowly escape serious injury in Hungary when the car he was travelling in collided with wild boars!
He did impress in the reserves at Newcastle and also won his first cap for Hungary against Lithuania.
Dubbed as an eastern European whizzkid, the attacking left-back arrived from one-time Hungarian title winners Zalaegerszeg after successful talks with Keegan.
It was actually Sam Allardyce who had ordered Kadar should be scouted but after Big Sam had been shown the St James’ Park exit door, Keegan was appointed and took over the discussions before giving the transfer the green light.
At that stage a relaxed Keegan probably thought that Kadar would be the first of many signings of his second coming as boss.
However, no sooner had Keegan been appointed, controversial transfer chief Dennis Wise was placed above his head and he effectively lost control of arrivals at United.
If it was supposed to be some type of football masterplan by Newcastle, it was quickly shortlived.
Keegan was renowned for doing his own work in the transfer market, and he was rather good at it too.
Manager Keegan had vowed to give youngsters like Kadar a chance. One night he stood behind the goal at North Shields to watch the likes of Kadar in action, as a certain Andy Carroll proved he could mix it up at senior level.
Keegan said afterwards: “This period is a great chance to try out new things and see what people can do.”
However, it didn’t work out that way for Kadar at Newcastle and he was restricted to just 26 appearances in total for the Magpies.
The defender certainly had the technical ability and could attack, but seemed to lack the physicality to survive in English football.
After watching Keegan, Joe Kinnear, Alan Shearer and Chris Hughton all come and go, the final say on his Newcastle career ended up in the hands of Alan Pardew.
The now Crystal Palace manager never seemed convinced by the Hungarian.
Kadar then headed for Roda JC in Holland, playing 11 games before being loaned to Hungarian side Diósgyőr, in the east of his native country.
Two solid seasons with Diósgyőr allowed Kadar to re-establish himself in his home country and after 40 appearances in Hungary’s OTP Bank Liga and impressing for the Magyars, he won a move to Lech Poznań in Poland.
With 28 caps now in the bag for Hungary, Kadar will be a guaranteed starter for his country in the finals in France.
Now 25, Newcastle fans got a glimpse of Kadar as a bulked out, no-nonsense defender as he kept Hertha Berlin’s Per Skjelbred quiet during Hungary 3-1 win on aggregate, dumping Norway out of the European Championships.
Like Hungary’s team in general over the last two years, Kadar has grown in stature.