Sylvester Stallone Kicks Off Filming 'This Is Us' With Milo Ventimiglia, Chrissy Metz and Justin Hartley: Pic

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Sylvester Stallone has officially joined This Is Us. There was just one problem on his first day -- cellphone coverage!

The legendary actor began filming the hit NBC series in Santa Clarita, California, on Saturday, and while he managed to document his exciting new role on social media, getting online proved a mission.

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“The irony is we can get Wi-Fi in Bulgaria, surrounded by wolves, but we can’t get it in Santa Clarita,” he said in an Instagram video, while panning to show his co-star, Chrissy Metz, getting lint removed from her outfit.

The star continued to humorously vent in the caption for the video.

“THIS is one of the great mysteries in MY life!!!” he wrote. “We can travel to the far ends of the UNIVERSE, yet, it's hard to find a decent local cell site!????! A MINI CELL PHONE HORROR movies starring Sylvester Stallone and Chrissy Metz ... and thank you Dan Fogelman you have created a great show. #thisisus @chrissymetz.”

While he couldn’t get enough signal to post his video until Sunday, Stallone did manage to upload a series of pics from set on Saturday, including a shot with his “good buddy” Milo Ventimiglia, whom he credited for inviting him onto the series.

Another snap showed him getting punched by Metz, while a third showed him dressed matchy-matchy with hunky co-star Justin Hartley. Stallone will share a pivotal storyline with Hartley's character, Kevin, in This Is Us' upcoming second season.

“On the THIS IS US set with Justin Hartley, this is a fantastic show and he is great to work with!” Stallone wrote.

Stallone is guest starring as Hartley’s character Kevin’s dad in the upcoming second season.

– who previously worked with Stallone on 2006's Rocky Balboa – recently talked to ET about having the 71-year-old star sign on for a role.

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“It's nice to know that the material attracts the greats even like Sly,” he said. “And to know that he'd want to be a part and play with us, it's a very good feeling, so we're thrilled."

"I'm personally excited, too, because his character's involvement gives Jack a lot,” Ventimiglia added. “Because you imagine if Sylvester Stallone is Kevin's movie idol, where'd he learn that from? Probably from Jack, probably from dad."

See more from the interview below.

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