When the interest rate of currency AAA increases while the interest rate of currency BBB remains constant, the forward rate for the currency pair, AAA/BBB, is expected to decrease. This is based on the interest rate parity theory, which states that the difference between the forward exchange rate and the spot exchange rate should be equal to the interest rate differential between the two currencies.

In this case, since the interest rate of currency AAA has increased, and the interest rate of currency BBB remains the same, the interest rate differential between the two currencies widens. To maintain interest rate parity, the forward rate for AAA/BBB must decrease.

Mathematically, this can be illustrated using the covered interest rate parity formula:

$\text{Forward Rate} = \text{Spot Rate} \times \frac{1 + \text{Interest Rate BBB}}{1 + \text{Interest Rate AAA}}$

As the interest rate of currency AAA increases, the denominator in the formula will increase, leading to a decrease in the forward rate.