Speaking just minutes after he heard the news, he said: "The news has just broken and I think it will come as a total shock to all of the players at the club.
"We only trained yesterday morning and we were delighted to have got that important win under our belts to make sure that we were nice and safe in the league, so we could build on that next season.
"As far as I'm concerned it is very disappointing to see Harry leaving West Ham; from a personal point of view he has been absolutely superb to me, which is something I've said time and time again.
"He has probably left West Ham with the strongest squad we have had for a number of years and I think he will be greatly missed by the club."
Stuart says his thoughts are with Harry and that any implications for his own future are secondary, adding: "I don't know what situation it leaves me in at the moment and if I was younger it would worry me.
"But as it is, I am a million years old, out of contract after one more match for West Ham, and so I will sit tight to wait and see what is next."
His managerial ambitions are well-documented but he did not wish to comment on whether he may be interested in the post, saying simply: "Out of respect for Harry, I wouldn't even answer that question. I have just become aware of what has happened and as far as I'm concerned he has been fantastic to me."
He praises Harry's work at the club and says: "You have only got to look at the young talent at this club with a midfield trio in the England squad and Rio Ferdinand having just left for £18million, and that is disregarding all the idiots like myself that have been deemed to be no good at all that have come in and done a job.
"He was definitely one to take a chance on people and more often than not, it paid off. He has done a hell of a lot for this club and I think he will be missed more than people realise.
"Harry is West Ham through and through and absolutely loves the club - his name will always be associated with West Ham United Football Club.
"He has had the hump that results have not been going well of late but everyone associated with the club should have.
"I know the result on Saturday came as a big relief to him but if it is solely a results situation, he has decided to walk away.
"It will be very strange in the next couple of weeks with everything up in the air, but that is always the situation when there is a transition."