The New Kids on the Block singer has urged the foursome - comprised of Harry Styles, Louis Tomlinson, Niall Horan and Liam Payne - to get back together as soon as possible following their extended hiatus otherwise their chances of achieving the same success they have done over the past five years will diminish dramatically.
Speaking to The Daily Star newspaper, he said: ''They were pretty great, they were all really great vocalists individually. I would love to see them reunite, they were sort of reaching heights that very few bands, let alone boybands, ever reach.
''In my opinion they were just starting to climb, it seemed like it was just the beginning. It's very sad that they ended it so quickly because I do think they were just about to hit great success. I can't say that they should have stuck together as I'm sure they had their reasons to separate but it would have been brilliant and I honestly think if they respect each other enough and give each other time the they will return and the reunion will be crazy.''
However, although he'd like to see them get back together, the 47-year-old star has admitted he has high hopes for Harry and his solo career.
He explained: ''I wouldn't say I am a Directioner, but I think Harry has some really good music coming out soon.''