The Nigerian teenager recently ended his spell with the Swedish club after completing a five-year move to the Premier League side on Saturday.
He will officially join Brighton at the Amex Stadium when the transfer window reopens later this month, subject to regulations.
Yohanna thanked everyone at AIK for their support saying their backing was vital in shaping his progress and helping him enjoy a successful and memorable time in Sweden.
” Almost a year ago, a dream came true when I signed my first first-team contract with AIK. From my first day at AIK, I have enjoyed every second, but now another dream has also come true,” he was quoted by AIK’s official website.
“Even though I am now leaving AIK, I will always carry with me what the club has meant to me and my development both as a footballer and a person. Thanks to all the players, managers and supporters who have supported me.”