From 1968 to 1974, Desi Arnaz and his sister Lucie co-starred opposite their mother in Here's Lucy as her children. In 1968, he had a guest-starring role as Jerry and Suzie's drum-playing friend Tommy in the episode, "The Hombre Who Came to Dinner: Part 2," from the show The Mothers-in-Law, executive-produced and directed by his father. In 1970, he appeared on The Brady Bunch episode "The Possible Dream." His best chance at enduring Hollywood fame came in 1973, when he played the title role in the film "Marco," a musical about the life of adventurer Marco Polo. However, like most Hollywood musicals of that period, it failed to register at the box office.
Arnaz has a daughter, Julia Arnaz, from a relationship with model, Susan Callahan-Howe, in 1968 when they were both 15 years old; Julia's relationship to Desi Jr. was proven by a paternity test in 1991.