The 'Firework' hitmaker delighted her boyfriend - who reached the milestone age on Friday (13.01.17) - with a star-studded bash in Palm Spring, California, on Saturday (14.01.17), at which they were joined by a host of pals, including Amanda De Cadenet, Jennifer Aniston and her husband Justin Theroux.
But the highlight of the evening for the British actor was a surprise appearance from his mother.
He shared a photograph of them embracing on Instagram and wrote: "Best gift ever surprise visit from me mum.(sic)"
Pictures shared on social media showed a number of the guests, including the 'Lord of the Rings' star and his mother, had donned onesies printed with Orlando's face for the celebration, but at one point, the actor and a number of his pals - including Justin - stripped down to the waist and posed for topless pictures.
The 'Roar' singer - who showed off her new blonde locks at the party - shared a video of the surprise party on her Instagram Story, which featured Orlando surrounded by his friends and family as he blew out the candles on his huge birthday cake, which was topped by a life-sized owl and had 'Happy Birthday Lando' written on it.
It was previously claimed the 32-year-old singer has hired a celebrity concierge service to plan 12 months' worth of events to celebrate Orlando's birthday.
A source said recently: "Katy is determined to make this year the best ever and is not letting money get in the way. She wants a combination of holidays and 'bucket list' experiences, including seeing some of the world's most famous sights."
The grand gesture comes just 12 months since the singer was spotted getting close to the 'Pirates of the Caribbean' actor - who has six-year-old son Flynn with ex-wife Miranda Kerr - at last year's Golden Globe awards, which alerted the world to their blossoming romance.
Katy isn't shy of making big gestures as gifts as back in 2010 she bought her ex-husband Russell Brand a trip to space when he turned 35.