The lion exhibit had one male and two females. Both females had litters a few months ago, but the cubs weren't on display yet (did see them on the webcam in the visitor's center though).

The cubs finally met this lion a few weeks after our visit. From the National Zoo webpage:

On December 1, Luke had his first introduction to his cubs. When the keepers opened the door separating the adults and cubs, and all seven cubs rushed through the threshold, eager to finally meet their dad. His face was priceless—clearly a bit overwhelmed and fearful. Luke responded to the cubs exactly as we expected: he ran from them and jumped on the bench as though they were mice under his feet—like elephants do in cartoons!

More here on the interesting interactions in the pride:

Cub introduction