Los Angeles, California - Billie Eilish has treated fans to a special surprise by dropping new merchandise in honor of her 22nd birthday.

The pop star turned 22 on Monday, and she made sure to include her fans in the festivities with a brand-new piece of merch.

The gray sweatshirt, which is called Billie's Birthday Crewneck, features "AM I ACTING MY AGE NOW?" written in bright red text and Billie's signature Blohsh logo on the back. Fans can get their own from her website now for $90.

Some fans have put forth theories that the text is a lyric from her upcoming third album, which she recently teased is "almost done."

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On her Instagram story, Billie teased her birthday celebrations with a blurry snap of a lit candle on a cupcake with the caption, "somebody is 22."

The Grammy winner's final week of being 21 was quite a memorable one, as she made a grand return to 30 Rock to perform as the musical guest on the latest episode of Saturday Night Live.

Billie debuted her smash-hit Barbie movie feature What Was I Made For? as her first song of the night. She was joined on stage by her brother, Finneas, who co-wrote the song with her.

The pair concluded the evening with a cover of Have Yourself a Merry Little Christmas.

Along with her performances, Billie showed off her acting chops in a skit with the night's host, Barbie star Kate McKinnon.