Celtic have signed attacker Sead Haksabanovic from Rubin Kazan on a five-year-deal.
The Montenegro international was wanted by four clubs but has opted for a move to the Scottish Premiership champions.
Haksabanovic, 23, made just two cup appearances during his three-year spell at West Ham from 2017, has most recently been training in Sweden after a loan spell at Djurgarden and did not want to return to Russia.
He becomes Celtic's eight summer signing, with Jota, Cameron Carter-Vickers, Alexandro Bernabei, Aaron Mooy, Benjamin Siegrist, Moritz Jenz and Daizen Maeda also joining.
"It feels amazing," he told Celtic TV. "What I know about Celtic is only good things and I'm very happy to be here.
"I heard about it around a month ago and as soon as I heard that Celtic wanted me I said to my agent that he had to make it happen because this is where I want to play.
"It's an amazing club with good players, fans and history. I've been watching some games and I think the team play in the same style as me.
"The team are doing great and I want to be part of that and make the fans, the club and myself happy."
What can Celtic expect from Haksabanovic?
Capped 28 times for Montenegro, Celtic's new number nine has also outlined what the fans can expect from him.
"I'm a playmaker with some flair. I'm good in one-on-ones, I have a powerful shot, I'm quick and I'll give everything for this club," he said.
"I know that Henrik Larsson is a big legend here and I know his son really well.
"Hopefully I can do something similar to him which is very hard to achieve but I'm going to try my best.
"I know Joe Hart and Albian Ajeti from West Ham and I spent some time with Carl in Russia.
"He saw somewhere that I was linked to Celtic and he wrote to me but I didn't want to say too much, I just asked him about the club and he only said good things, so I can't wait to get started now."
Celtic interested in Atanasov
Sky Sports News understands Ange Postecoglou could yet further add to his side before the window shuts, with Hajduk Split defensive midfielder Jani Atanasov also of interest.
With around one week to go until the transfer window closes, Postecoglou insists the club will move for the right player.
"Our recruiting this year has been around making our squad better and more robust, compared to last year," he said.
"If you look at the players we've brought in, that's what they've added to our squad.
"So it's not a specific area as such, it's more if we can get a couple of players who can play a couple of positions it will help us."