Task: Question Answering
Input (English): Passage: In September 2010, Mikael Åkerfeldt stated that he was writing for a new Opeth album. The band announced on their website that they would start recording their tenth album on January 31, 2011, at the Atlantis/Metronome studios in Stockholm, once again with Jens Bogren (engineering) and Steven Wilson from Porcupine Tree as co-producer.Shortly after mixing was complete on the new album in April 2011, Opeth announced that Per Wiberg was relieved of his duties in the band.
In the press statement, Mikael Åkerfeldt explained the decision, saying, "Mendez, Axe and Fredrik and I came to the decision that we should find a replacement for Per right after the recordings of the new album, and this came as no surprise to Per. He had, in turn, been thinking about leaving, so you could say it was a mutual decision. There's no bad blood, just a relationship that came to an end, and that's that."Opeth's tenth album, Heritage, was released on September 14, 2011, to generally favorable reviews. The album sold 19,000 copies in the United States in its first week of release and debuted at number 19 on the Billboard 200 chart. Heritage debuted at number four in the band's native country of Sweden.Heritage became the second Opeth album to not feature any death growls and had a much more progressive style than previous albums from the band, something that Åkerfeldt had been wanting to do for some time.The first two songs Åkerfeldt wrote for Heritage were in the style of Watershed. After hearing the songs for the first time, Martín Méndez told Åkerfeldt that he would be disappointed if the album continued in that direction. Relieved that Méndez was not interested in doing another conventional Opeth album, Åkerfeldt scrapped the two songs and started the writing process over in a different style. In the press release for Heritage, Mikael Åkerfeldt revealed that he felt as though he had been building to write the album since he was 19 years old. In a review for Allmusic, Thom Jurek called Heritage the band's most adventurous album, describing the songs as "drenched in instrumental interludes, knotty key and chord changes, shifting time signatures, clean vocals, and a keyboard-heavy instrumentation that includes Mellotrons, Rhodes pianos, and Hammond organs".Opeth supported Heritage with a tour that would last for over 200 tour dates. The tour was the band's first with new keyboardist, Joakim Svalberg, who played on the opening track of the album. During the tour, Opeth played with bands such as Katatonia, Pain of Salvation, Mastodon, Ghost and Anathema all over the world in countries such as the United States, Europe, Turkey, India, Japan, Greece, Israel, Latin America and Sweden. The tour concluded with "Melloboat 2013". 
Question: What is the last name of the person who was not surprised that the band was looking for a replacement for him?
Output (English): Wiberg.