Happy birthday Twitter: 8 most memorable celebrity tweets

After winning a second presidential term in November 2012, Barack Obama posted this photo to Twitter with the caption “Four more years.” It was the most retweeted photo ever, until Ellen Degeneres broke his record during the 2014 Academy Awards with her star-studded “Oscars selfie.” "I thought it was a pretty cheap stunt,” he later joked to Ellen.

During the 2014 Academy Awards, host Ellen wrangled an impressive number of actors from the audience to pose for an all-star selfie. The snap, which included stars like Jennifer Lawrence, Meryl Streep, Bradley Cooper, Julia Roberts, Channing Tatum, Brad Pitt, Lupita Nyongo and Kevin Spacey, has been retweeted more than 3.4 million times!

The news of a royal birth was delivered by Clarence House’s official Twitter account. “Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 4.24pm,” it read. The Queen and Prince Philip also used Twitter as a means to express their joy, writing that they were “delighted at the news of the birth of The Duke and Duchess of Cambridge's baby.” Consequently, “Royal baby” was among one of the hottest Twitter topics of 2013.

In what was to be the most mind-boggling Twitpic ever, Canadian astronaut Chris Hadfield shared this beautiful photo of the moon – from space!

The world was privy to Amanda Bynes’ mental health issues last year, a result of her regular and increasingly bizarre Twitter updates. After posting a series of confusing and controversial messages, in which she lashed out at fellow stars she deemed ‘ugly’ and bemoaned her inability to lose weight, the star was finally admitted to a psychiatric hospital where she was diagnosed with schizophrenia and bipolar disorder. She is currently doing well and is on the road to recovery.

Pope Francis made international headlines when he joined Twitter one year ago – a surprisingly modern move for what many consider to be the leader of an antiquated institution. “Dear friends,” he wrote. “I thank you from my heart and I ask you to continue to pray for me. Pope Francis.

Celebrity feuds have taken on a new form with the advent of Twitter, and no feud was quite so ugly as the one between Miley Cyrus and Sinead O Connor last year. “Sinead. I don't have time to write you an open letter cause Im hosting & performing on SNL this week,” Miley wrote in response to a scathing note that Sinead had penned, in which she criticized the pop star for her scintillating sex appeal.