#2YearsOf1D has gone trending on Twitter as One Direction fans (and Niall Horan) shout out the hashtag on the microblogging site.

1D fans are shouting out their love and congratulations on Twitter for the hottest boy band today. They are happily reminiscing - in 140 characters or less - how it all started for their adorable young idols.

On July 23, 2010, reality show icon Simon Cowell put together a group of male singers who initially went out to compete individually in a pop talent competition. The rest is history. And that history has been chronicled by fans on Twitter through many shows and media appearances of One Direction.

One Direction, Reminiscing Two Years

Here is a photo of how the lives of Zayn Malik, Niall Horan, Liam Payne, Harry Styles and Louis Tomlinson have changed forever. And here are tweets to match that image:

@saini_175: #2yearsof1D july 23rd 2010 at 8:22pm, contestants #165998 #232677 #165616 #155204 #61898 were formed into now the worlds biggest boy band.

@ILOVE1D16: Louis: 155204. Zayn: 165616. Liam: 61898. Niall: 232677. Harry: 165998. Happy Birthday One Direction. #2yearsOf1D. :')

1D Fans - Best publicists?

Time has shown that 1D has no better publicist than the fans themselves. If all the love and support 1D could be put in a jar, there will not be enough jars in the world.

Niall Horan and the rest of the giant group become more endearing to fans as they do not fail to tweet back the love when they get a chance. Here is a tweet from Niall using the same trending hashtag.

Niall Horan tweets #2yearsOf1D (Image: Twitter screen cap)

Here are some of the most loving tweets from 1D fans.

@all1d: The formation of One Direction was more important than the formation of earth. #confirmed #2yearsof1D

‏@About1D_: #2YearsOf1D They made us cry, laugh, dream.. But most importantly, they made each one of us feel special. We're part of a family #1DFamily

@onlyanother_fan: #2YearsOf1D i can't even describe what i feel. These five boys will be forever in our hearts. Once a Directioner, always a Directioner.

Some tweets are centred on the boys' achievements in two years.

@loovezayn: It's 2 years ever since One Direction has been formed, and it's incredible to think how far they've gotten in such little time. #2yearsof1D

@EleanorlJCalder: #2yearsOf1D Very Proud of the Lads, They Make people smile everyday. Very Proud.

@UpToDate1D: So much has happened, they've achieved SO MUCH yet have much more ahead of them! Thank you so much 1D for everything :) !!