Citi is the first digital custodian to join the exchange, which launched back in 2020 under the name Bondevalue.

The fractional shares concept uses blockchain technology to divide assets or securities into smaller constituents that can be held on a blockchain register.

It is seen as a way to make illiquid, real assets such as real estate or fine art, much more accessible to wider range of investors.

For BBX, its exchange is designed to bring many of the benefits of equity trading to the fixed income world in terms of accessibility and trading. The arrival of Citi will now add a settlement and custody function to the platform.

"Digital custody is the next big step in the transformation of the bond market, making bond markets, more transparent, electronic and accessible to all," said Rahul Banerjee, CEO and co-founder of BBX.