SPOILER WARNING: This article contains major spoilers for "Therefore She Is," the latest episode of The Flash.

The Flash just revealed a major new clue about the show's Mystery Girl, who debuted in the four-show Arrowverse crossover "Crisis on Earth-X." At the end of "Therefore She Is," the latest episode, Mystery Girl turned up with a baby shower gift for Joe and Cecil, only to disappear -- with a little help from her super speed, of course.

In the tag for the episode, Mystery Girl masqueraded as a delivery girl. She handed Cecil a diaper bag, saying that the gift must be from someone who realizes time is precious. She also offhandedly mentioned that it looked like Cecil would give birth in 21 days -- which is, coincidentally, the date of the Season 4 finale. She also cast Iris and Barry a significant look before the scene cut away from her.

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When Joe and Cecil turned to ask if the gift had come with a note, Mystery Girl had disappeared, but she hadn't gone far. She was simply around the corner, listening to their voices. She then closed her eyes and ran away, revealing that she is a speedster. Unlike other speedsters, the trail of lightning she leaves in her wake is a combination of colors: red, blue and yellow.

Since she is a speedster, it's very possible that Mystery Girl is from the future, as speedsters have the ability to travel through time. This would explain why she knew exactly when Joe and Cecil's baby will be born and how she knows the Speed Force script that Barry wrote in after he escaped his imprisonment.

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However, that implication carries a much darker prophecy: the death of Joe and Cecil. When she told them time was precious, she suggested that she is not, in fact, Barry and Iris' daughter, as many have assumed. Instead, she hinted that she is actually the daughter of Joe and Cecil, who -- coincidentally -- are expecting a baby girl. By emphasizing that time is precious, she implied that Joe and Cecil won't be much longer for this world. Judging by her previous stare-down with Caitlin and Harry, one of their friends may even be responsible.

In the comics, Barry and Iris had a daughter named Dawn Allen after they retired to the 30th century. Both she and her twin brother Don inherited their father’s speed. They never met their father, who died before their birth in the events of Crisis on Infinite Earths, but soon followed in his footsteps to become Speed Force heroes known as the Tornado Twins. However, The CW's The Flash may transfer this origin over to Joe and Cecil's daughter instead.

Airing Tuesdays at 8 p.m. ET/PT on The CW, The Flash stars Grant Gustin as Barry Allen, Carlos Valdes as Cisco Ramon, Danielle Panabaker as Caitlin Snow, Candice Patton as Iris West, Jesse L. Martin as Joe West, and Tom Cavanagh as Harry Wells, with guest appearances from Keiynan Lonsdale as Wally West and Hartley Sawyer as the Elongated Man.