While Zayn sensationally quit the group earlier this year, Liam still made a point of acknowledging his part in making them so successful since they were first formed on the UK 'X Factor'.
Liam wrote: ''Wowwwww 5 years 5 boys what an amazing journey I couldn't thank you all ever enough and thank you Louis, Niall, Harry and Zayn for everything (sic).''
Zayn responded by retweeting the message for his own followers to see and writing ''thanks bro'', with a smiley face emoji.
And Liam added another message which seemed to include Zayn, writing: ''Thanks for all the memories boys I love you all.''
Niall Horan also celebrated the anniversary, taking to Twitter to thank fans.
He wrote: ''5 years, literally sitting down talking about last night. Insane! I remember the day we were out together like it was yesterday!
''Thank you so much for what you've done for us so far, what an incredible journey it's been, wish we could thank you all.
''You guys have changed our lives and we all love you so much! Best fans on the planet, easy!(sic)''
Harry Styles wrote an emotional message, tweeting: ''We have been a band for five years. And it is impossible to thank anyone enough for all the support they have given us over this time.
''All the crew that we have been so lucky to work with, and everyone who is behind the scenes. We thank you for everything that you do.
''To you who support us, in any way, thank you. We wouldn't be here without you. You did this and we thank you for having us. All the love.''
And even dad-to-be Louis Tomlinson broke his recent Twitter silence, writing: ''Every single day we are thankful for the platform that you incredible people gave us. What an amazing 5 years it's been!!
''You have been by far the most incredible fanbase and nothing you do goes unnoticed. We are so lucky to have you guys! Thanks so much :)
''Thank you thank you thank you thank you thank you thank you thank you thank you thank you thank you thank you thank you thank you thank you.
''My attempt of expressing how thankful we are for you guys!(sic)''
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