The Basingstoke-born back recently started the LV=Cup fixture with Bath Rugby at The Recreation Ground and has now committed his playing future to Blues by signing a deal until at least 2015.
Humberstone started his rugby career in the Harlequins Academy, gaining representative honours with South East England and England Students.
Following a season spent playing with Heriot RFC in the Otago province of New Zealand, Simon returned to the UK to study at UWIC.
Humberstone's growing reputation attracted the interest of a number of clubs during the summer of 2010, but he linked up with Pontypridd RFC and has been a key part of the club over the last few seasons.
Director of Rugby Phil Davies said: "Simon joined up with us last year when we were looking for fly half cover and did brilliantly.
"He was fantastic in the LV=Cup win over Ospreys and the Munster game in the RaboDirect PRO12 was also a very good experience for him as it showed him what is required at this level.
"Simon is an intelligent player and this is a big opportunity for him to be part of our set-up. It's exciting for him and it strengthens our squad at outside half, which is crucially important to us going forward."
Humberstone admitted signing the full-time contract with Blues was a dream come true.
"I got a taste about what it was all about back in November in the LV=Cup and after that whets your appetite it is all you want to achieve," he said.
"Being here with Dale McIntosh and Paul John, who I know so well from Pontypridd, makes the move even more enjoyable and I'm determined to make this a success.
"Just being around world class players on a full-time basis improves your game, you have to deal with the intensity just in training and the pressure it puts on your skill set. It makes you a better player.
"It's unfortunate for Rhys (Patchell) at the moment as he is out injured after such a good season, but it gives opportunities for players like me and Gareth Davies to put a marker down for the number 10 jersey."
Humberstone also paid a special tribute to Pontypridd for their understanding and support over the last three and a half years.
"I owe a massive debt of gratitude to Ponty for all they have done for me. It's a special club with fantastic fans and a superb coaching staff. I wouldn't be where I am today without them so I wish them every success for the future."