Guimaraes was in tears as he said an emotional goodbye to teammates at the club's pre-season training camp in La Manga before travelling for his medical, becoming the third senior player to leave St James' Park this summer following the departures of Sandro Tonali and Anthony Gordon.
Newcastle United chief executive David Hopkinson insisted the fee, though below Arsenal's initial hopes, represented good business for the club.
"It was not the fee that I think Arsenal had hoped to pay and of course we would have liked an even higher number," he said.
"But I think you're dealing with sophisticated actors on both sides and that's what negotiation looks like. It's a fee that satisfies us.
"If you want to put a merchandising spin on it, it's the highest fee for a player in that position at that age. Is that a good deal for Newcastle? I believe it is. But Arsenal is getting a very special player and special person so this works from a financial perspective for both sides."
Sporting director Ross Wilson was candid that selling the captain had never been part of Newcastle's plans for the summer.
"We didn't want to sell Bruno. It wasn't in the plan to sell Bruno. None of us - or ownership - wanted to sell Bruno. He's our captain, he was very, very important to us," Wilson said.
He explained that the club's hand was ultimately forced by the player's own wishes.
"What we had to weigh up was, very respectfully from Bruno with his behaviour towards us, very emotionally as well, effectively told us he wanted to leave and move on. That doesn't mean he can go but it certainly plays a part in what our thinking is when we hit a certain range of number. But there's no part in saying it was part of our strategy and was in our thinking this summer - it wasn't. We can only be honest about that."
Guimaraes, 28, joined Newcastle from Lyon in January 2022 and made 195 appearances for the club, scoring 31 goals and helping the Magpies win the Carabao Cup in 2025, their first major domestic trophy in 70 years.
His departure gives new manager Matthias Jaissle, appointed following Eddie Howe's exit, funds to reshape a squad already boosted by five new signings this summer. Wilson confirmed the club intends to reinvest the proceeds.
"We want to strengthen the squad. Of course we want to add more. Matthias wants to assess what we have as well, which is obvious, he's been doing that for some time now so he's got a view on that already and we're aligned on what we want to do."