With their Group A game with Romania locked at 2-2 in the 88th minute, Henderson let a long-range shot from Florinel Coman squeeze past him at the near post.
Conan then made sure of the win with a late fourth after game that burst into life in a frantic final 15 minutes.
George Puscas open the scoring from the penalty spot in the 76th minute but Demarai Gray hit back immediately with a superb curling effort.
Ianis Hagi restored the Romanians’ lead after an error from Fikayo Tomori in the 85th minute but Tammy Abraham restored parity one mine later.
But in the moment that the game will be remembered for, Henderson was made to pay for his error by Coman who made doubly sure of England’s premature exit from the competition.
And fans of a number of clubs, including United, took to social media to vent their frustration at his display.
Henderson spent last season on loan at Championship side Sheffield United and one fan said on Twitter: “Henderson ushered in two goals, send him back to Sheffield.”
Another added: “Dean Henderson let’s in a howler, commentator ‘that’s a real surprise’ we’ll no it’s not is it, he’s made about seven of them this year, it’s part of his game.”
A third agreed: “So, this is the first time I have seen Dean Henderson in goal & he‘s been shocking for all three of Romania‘s goals.”
Henderson spoke about replacing David de Gea – who endured a difficult time of his own last term – at United next season in the build-up to the Romania game.
Another fan said on Twitter: “Dean Henderson mouthing off saying he’s ready to be United’s number one, looks perfect for it.”
“Dean Henderson with a De Gea-esque howler,” another added.
Another agreed: “Dean Henderson with his best De Gea impression.”
“Can tell Dean Henderson has been studying De Gea closely,” said another.
Another said: There are real United fans that think Dean Henderson is better than De Gea because he was doing stunts in the Championship.
“You all deserve relegation.”
