Held at Espacio Mad Cool – home to the festival since last year – in the north of the city, the event will take place on Wednesday 10 July, the day before the full festival commences.
Topping the bill are two acts worthy of headlining festivals in their own right – British metalcore favourites Bring Me The Horizon, and arguably Spain's biggest musical export of recent years, flamenco-pop superstar Rosalía.
They will be joined on the day by Lykke Li, The Cat Empire, Metronomy, The Amazons, Viagra Boys and more. See below for full lineup and more details.
Tickets for the Welcome Party will go on sale on Friday 19 April.