The two were pitted against each other in Thursday's draw in Monaco, with Manchester City and CSKA Moscow completing a tough-looking Group E.
Benatia sealed a move from the Stadio Olimpico to the Bundesliga champions on Tuesday but will not have to wait long to meet his old team-mates on the field again.
"I was really hoping to come up against AS Roma and see some of my old friends," he said.
Bayern faced both City and CSKA in last year's pool phase and qualified top of the pile with five wins from six games, but Germany striker Thomas Muller is expecting a tough test.
"We know most of our opponents from last year. It will be a very demanding group," the World Cup winner said.
Matthias Sammer, sporting director at the five-time European champions, added: "It's a very attractive and very difficult group, but it's the right kind of challenge for us."
Pep Guardiola's men reached the semi-finals last season but were humbled by eventual winners Real Madrid, losing 5-0 on aggregate to Carlo Ancelotti's side.
