This is the 13209th most frequent German word.
aufgefallen
"Noticed" or "attracted attention."
'aufgefallen' here means 'noticed' or 'became aware of' and is used in reflexive form with 'mir' to imply the noticing was done by the speaker.
Mir ist aufgefallen, dass er früh gegangen ist.
I noticed that he left early.
In this example, 'aufgefallen' conveys the act of becoming aware or noticing something for the first time, paired with 'nie' to indicate this realization hasn't happened previously.
Es ist mir nie aufgefallen, wie schön dieser Park ist.
I never noticed how beautiful this park is.
Here, 'aufgefallen' is used in a question form through inversion, asking if someone has noticed or become aware of the flickering light.