The project was unveiled on 22 April 2014 and was described by Lucassen as "an epic double concept album, a combination of 'classical meets metal' and 'acoustic folk'." Lucassen's most recurrent collaborator Ed Warby will be featured once again on drums, and it will be his very first album featuring a double bass among the instruments. He confirmed that Johan van Stratum from his former band Stream of Passion would play bass on the album. Also, due to "unforeseen problems", Warby had to re-record all his drum parts in one day only. Other former collaborators will be back, such as Joost van den Broek, Ben Mathot and Maaike Peterse, along with two new guest instrumentalists: Hinse Mutter and Jenneke de Jonge. On September 2, 2014, Lucassen revealed that his collaboration with van Giersbergen was actually a new band, called The Gentle Storm. He stated that van Giersbergen would perform live with band next year, possibly ruling himself out of live shows. On October 10, it was announced at The Gentle Storm's official Facebook profile that the album would be composed of two CDs with the same songs, but recorded in totally different arrangements. CD 1 will be "the 'Gentle' album, all acoustic and folky with lots of exotic instruments", while CD2 will be "the 'Storm' album, an all-out, bombastic orchestral metal album". The post also stated that there would be "plenty of progressive elements mixed in". The post invited fans to ask questions, and some of the answers revealed that the album is set for a March 2015 release, that the band will probably continue if the public reception is good enough and that the concept will be "a historic love-story". On 4 November, the album was revealed to be titled The Diary, with a cover art by Alexandra V. Bach, who also drew the art of A War of Our Own by Stream of Passion, another band started by Arjen, but that continued after he left it. On January 20, 2015 the project released two lyric videos for both versions of the song "Endless Sea". The Gentle Storm did a small-scale tour in April 2016, after which Lucassen and Van Giersbergen focused on other projects, including together in the Ayreon Universe series of concerts. Van Giersbergen subsequently created the band VUUR, mostly with live members of The Gentle Storm.
