This Is Us is adding a very familiar face in Season 4. Once Upon a Time alum Jennifer Morrison will be joining the NBC drama this fall in a recurring guest role, TV Guide has learned.

Details about who Morrison will be playing are being kept under wraps for the time being, but the actress will have a "substantial" role in the next chapter of the Pearson family saga, according to TV Line, which first reported the news. This marks Morrison's first TV role since leaving Once Upon a Time in 2017.

Even though the This Is Us producers aren't releasing information about Morrison's role at this time, that won't stop us from speculating from who she'll be stepping in to play. Here are our theories:

1. Kevin's (Justin Hartley) baby mama: Kevin had a preteen son in the This Is Us Season 3 finale, but he had just broken up with Zoe (Melanie Liburd) in the present day timeline, leaving a lot of people wondering how he ended up with a son. Does he adopt? Does he have a wife we haven't met? Considering how much Morrison looks like Kevin's first love, Sophie (Alexandra Breckenridge), she definitely fits his type.

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2. A dance teacher at Beth's (Susan Kelechi Watson) dance school: Season 3 ended with Beth realizing her life's dream of becoming a dance school owner. It's likely that we'll be seeing more of that as we watch Beth build the studio from the ground up — Morrison could be part of that dream.

3. Rebecca's (Mandy Moore) doctor/nurse: Rebecca was in pretty rough shape at the end of Season 3, which indicates fans will begin to see her downfall as Season 4 progresses. It could be that Morrison is playing someone who diagnoses or treats Rebecca for whatever condition she has in during the Season 3 finale. Anyone helping to guide the Pearson family matriarch through a difficult time would have a substantial role with the family.

Even though Morrison is only a recurring guest star right now, there is potential for whatever role she is playing to grow, as NBC renewed the drama for an unprecedented three seasons last month.

This Is Us returns Tuesday, Sept. 24 at 9/8c on NBC.

Jennifer Morrison, <em>Once Upon a Time</em>Jennifer Morrison, Once Upon a Time