  Double bars are thought to be important features for secular evolution in the
central regions of galaxies. However, observational evidence about their origin
and evolution is still scarce. We report on the discovery of the first
Box-Peanut (B/P) structure in an inner bar detected in the face-on galaxy NGC
1291. We use the integral field data obtained from the MUSE spectrograph within
the TIMER project. The B/P structure is detected as bi-symmetric minima of the
$h_4$ moment of the line-of-sight velocity distribution along the major axis of
the inner bar, as expected from numerical simulations. Our observations
demonstrate that inner bars can follow a similar evolutionary path as outer
bars, undergoing buckling instabilities. They also suggest that inner bars are
long-lived structures, thus imposing tight constraints to their possible
formation mechanisms
