The close friends headed down to London to watch West End musical The Bodyguard, in which Beverley Knight plays the lead.
Gemma told her Twitter followers that she was a huge fan of Beverly, and after the show, she got the chance to meet the British singer herself.
Gemma tweeted: "@Beverleyknight you are MAGICAL omg was in shock to meet you amazing singer amazing in @TheBodyguardUK speechless omg amazing."
Posting a photo of the trio backstage, Gemma said: "Best thing meeting @Beverleyknight since winning plus size fashion designer award this year so happy x."
It was quite the birthday treat for Harry, as Beverly even sung happy birthday to him - and the whole thing was recorded!
He tweeted: "Best birthday ever, and to top it off I've had the amazing @beverleyknight sing me happy birthday xx."
We think this is a birthday memory that Harry will treasure forever!
Harry got tons of birthday messages from his close friends and cousin Amy Childs, as well as a tweet from TOWIE's Bobby Norris, who said: "@MrHarryDerbidge happy birthday babe, can't wait to see you later #dinner #cocktails x."
After the theatre, Harry headed down to Balans in London, where he was joined by Gemma, Bobby and friends.
Boutique owner Harry was later seen leaving the venue with a large personalised birthday balloon, which read on the back: "love Bobby xxxx".
The balloon also had the initials "H+B" printed with purple love heart symbols. Taking to Twitter this morning (4 April), Harry said: "Had the most amazing day ever and to top it off, this was here waiting for me at the restaurant! @BobbyCNorris H+B x."
Last week, Bobby fuelled rumours that he is dating Harry by posing for a picture during a "cheeky" lunch date.
Just a week prior to that, the pair were pictured kissing while enjoying some drinks at a bar in Essex. Bobby recently admitted on TOWIE that he has got a new boyfriend, but has kept tight-lipped about the man's identity.
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Watch Beverley sing to Harry below: