Stellar shells around galaxies could provide precious insights into their assembly history .
However , their formation mechanism remains poorly empirically constrained .
We present MUSE @ VLT data of the most prominent outer shell of NGC 474 , to constrain its formation history .
The stellar shell spectrum is clearly detected , with a signal-to-noise ratio of around 65 pix ^ { -1 } .
We use a full spectral fitting method to determine the line-of-sight velocity and the age and metallicity of the shell and associated point-like sources within the MUSE field of view .
We detect six globular cluster ( GC ) candidates and eight planetary nebula ( PN ) candidates which are all kinematically associated to the stellar shell .
We show that the shell has an intermediate metallicity , [ M/H ] = -0.83 ^ { +0.12 } _ { -0.12 } and a possible \alpha -enrichement , [ \alpha /Fe ] \sim 0.3 .
This metallicity and the number of PNe are consistent with a progenitor galaxy more massive than 10 ^ { 9 } M _ { \odot } .
The photometry of the shell suggest that it is possibly composed of stars from the low metallicity outskirts of an intermediate mass ( \sim 1:10 ) companion .
We show that at least two globular cluster candidates are quite young , with ages below 1.5 Gyr , which gives a lower-limit for the merger age .
We note that spectroscopic data on the center of NGC 474 shows the presence of a young ( \sim 1 Gyr ) stellar population .
We conclude that the shell formation event is likely to be an intermediate-mass merger which happened around 1.5 Gyr ago and which has collaterally triggered the formation of massive , up to \sim 6 \times 10 ^ { 4 } M _ { \odot } , star cluster , and a nuclear starburst in NGC 474 .