Simple says that it will operate as a separate business within BBVA alongside the Spanish giant's other US operations, including BBVA Compass. It will also continue to be led by founder and CEO Joshua Reich.

Reich first pitched the idea of Simple to co-founder Shamir Karkal four and half years ago, spotting an opportunity in the widespread public disillusionment with traditional banks in the wake of the 2008 economic crisis.

With a strong background in technology, the founders believed that they could do better, and in the words of one-time CTO Alex Payne, build "a bank that doesn't suck".

After some teething problems, Simple finally opened its virtual doors 18 months ago, and now claims more than 100,000 customers with around $1.7 million in transactions.

Because Simple is not actually a bank, these accounts are actually with a FDIC-insured partner, Bancorp Bank, and will remain there "for the time being".

Having pitched itself as the young challenger, it is now joining the big boys, with Reich explaining in a blog post: "Working with BBVA gives us the resources, scale, and autonomy we need to accelerate our growth while staying true to our mission."

Reich says that BBVA is putting up "significant resources" and this will be used, in part, to bolster Simple's 92-strong team.

"We are entering an incredibly exciting time at Simple where we have the long-term resources and support to continue building a new global brand in banking. I am thrilled to begin this journey with our new partner!" he signs off.

BBVA, through its corporate venture arm BBVA Ventures, is actively investing in disruptive initiatives in financial services. Some of its current investments include SumUp, the Berlin-headquartered startup enabling mobile point of sale payments; Radius, a US-based company providing business insight into millions of small- and mid-size businesses; Freemonee, which analyzes its customers' transactional data to create relevant offers from retailers; Ribbit Capital, a financial technology-focused venture capital fund; and the seed-capital fund and accelerator program 500 Startups.

BBVA innovation centre director Gustavo Vinacua will be shedding more light on the bank's digital strategy as he joins an all-star line-up of speakers for Finextra Future Money, a two-day conference in April that will explore the new wave of innovation sweeping across the financial services sector.