list to dictionary conversion with multiple values per key?

I have a Python list which holds pairs of key/value:

l = [[1, 'A'], [1, 'B'], [2, 'C']]

I want to convert the list into a dictionary, where multiple values per key would be aggregated into a tuple:

{1: ('A', 'B'), 2: ('C',)}

The iterative solution is trivial:

l = [[1, 'A'], [1, 'B'], [2, 'C']]
d = {}
for pair in l:
    if pair[0] in d:
        d[pair[0]] = d[pair[0]] + tuple(pair[1])
    else:
        d[pair[0]] = tuple(pair[1])

print(d)

{1: ('A', 'B'), 2: ('C',)}

Is there a more elegant, Pythonic solution for this task?